I have an unsure ideal of what's good. I normally write in third person view and love to tell a story like a book but I'm curious how others prefer it and if I should try to write in 1st person too!

I think 3rd person allows people to look in and observe. Fitting 1st person in sometimes can be a little more personal, most effective with character asides, internal monologues and the like.

It also helps to write in the present, as opposed to the past. This creates a sense of urgency, otherwise more difficult to achieve.

I put 3rd, but my "backstory" is usually just a collection of bullet points.

I don’t think there’s an absolute right answer. Different stories call for different POV. 
It’s mostly up to what works for you as a writer. Some people have a hard time getting inside someone’s head enough for a good 1st person. Others need to do it to figure out their character’s personality. 
And if you’re starting at level 1, it should really be pretty short, to the point it almost won’t matter. There’s actually a whole long thread of 3-sentence backstories. 

This is one of those areas where there's no need for a prescriptive norm for the game or general or the specific player.  Whatever the player's comfortable with is what works.  

You're also missing 2nd person.  A lot of games outside D&D present pregens with a 2nd person backstory to help the player get into character.  Something worth experimenting with.

It really depends on your style I guess.

My opinion is that it should be able to be read out to its primary target audience without alteration and be appropriate to tell them the story. It's meant to tell a story to someone and not be an autobiography.

So for pregenerated characters, 2nd Person ("You were born...") is the most appropriate, since the primary function is to inform the player of who the character is.

For the vast majority of characters, the primary target audience is other players and the DM, who are a third party, and as such, 3rd person ("He was born...") is the most appropriate.

My background is in third-person writing so for both the game itself and for backstories I’ll always use third person, it helps me get out of my head and into my characters since I’m basically narrating them instead of acting as them. But it really depends on which mood you’re going for. Sometimes first person can be better for intrigue since a third person narrator is usually in a position of omnipotence with some detachment from the character in question.

A first person view also helps to build empathy but there are plenty of examples of exceptions to this. I like third person because I enjoy descriptive writing and you don’t really get that with a first-person perspective.

I usually write them in third person because that’s how I normally write, but it would be interesting to try first person for a change.

As a player,  my backstories are usually part first person and part third person.  The first person portion is a short in-universe speech, letter, missive, or other document created by my character to give the DM an idea of the character’s personality.  However, as the document is written by the character, it hardly counts as a reliable narration.  The third-person portion is the objective truth written by an impartial, omniscient narrator that can provide the DM information about the character’s story thus far, including information the character is not privy to.

I find this gives DMs the best of both worlds - the insight into the character’s persona from first person and the more reliable factual history of third person. 

In all seriousness, no-one else cares about your backstory, so write it the way you want to read it.

Backstory is the boring **** that happened before the game. Its only purpose is to remind you how you want to develop your character's personality.

As a GM if a player tries to give me their backstory document, I say "no". I'm not reading it. I want to see the character's personality come out during play. I might be interested in big points (for example, "has your character ever been in jail?") but I can ask those questions at the table as they come up in game (for exmaple, I'll have an NPC ask the character, "have you ever been in jail?").

I generally do it in third person, after selecting those background bullets (not always from the official background). That gives me a basis to build the story around. Also, as Xalthu was saying, unless it’s a high level character it should be short - enough to cover those blurbs you selected and to get them out of their home and adventuring. If far from home I often make them freshly paid off caravan guards - that explains why they are where they are, where they got their money and equipment and why they are now looking for work (as an adventurer). And that is about all most starting characters really need or should have. The more you have them do the more experience they should have and that means levels pretty quickly.

Quote from Greenstone_Walker >>

In all seriousness, no-one else cares about your backstory, so write it the way you want to read it.

Backstory is the boring **** that happened before the game. Its only purpose is to remind you how you want to develop your character's personality.

As a GM if a player tries to give me their backstory document, I say "no". I'm not reading it. I want to see the character's personality come out during play. I might be interested in big points (for example, "has your character ever been in jail?") but I can ask those questions at the table as they come up in game (for exmaple, I'll have an NPC ask the character, "have you ever been in jail?").

 I suppose it depends on your style of GMing, but I find that sort of thing quite useful; it provides a good source of plot hooks that the character ought to bite on. These can be either specific to the character (your beloved brother has been kidnapped) or just similar situations that speak to them (a former refugee given a chance to help other refugees).

For first-level characters, they ought to be pretty short, anyway, just "why are you adventuring instead of being sensible?", rather than "here are all the cool things I did before I joined the party!"

The backstory that I write and submit to the DM is written in 3rd person. This is partly because the whole thing is meant to be a collaborative effort between the DM and I... are all my ideas compatible with the world she created? How many NPCs can I introduce as part of my character's backstory? Did I give them access to too many resources that might unbalance the game? It's easier to adjust that stuff if it's in a passive 3rd person "voice" where everything is very matter-of-fact and doesn't have a lot of emotional embellishments.

However, once the character's basic history and background is written, I sometimes write down short stories in first person, either written as though it's a journal entry or almost like I'm writing it as if it's the character telling a story. This is both a writing exercise to help me get into the character's head a bit more, but also kind of a "script" I can use at some point in the game, just in case I have a story to tell that's important to the character so I can make sure I get all the details right. In one campaign I played as a bard, and part of that included having a lot of little stories to tell... either parables, or jokes, or just legends to share... leaning into the idea of being an entertainer without necessarily being expected to sing at the table.

Personally I usually go first person since I feel like it helps you get a better sense of your character. But I've seen a lot of people do it in a lot of different ways.

I think I did third person some when I was a lot newer to D&D, but I stopped because it felt like I was just an onlooker in my characters own back story, as opposed to the person who would actually be playing them.

It doesn’t really matter, whatever works best for each player is what’s best for them. I usually write my backstories in 1st person, but that’s just me.

A couple folks here have said they think backstories for low-level characters should be short - I think it is more accurate to say that they “should take into account the starting level.” That can still result in a rather long backstory, especially as many characters are at least in their 20s, so have a couple dozen years of history that could be covered.  I’ve had players go into incredible details on their family histories, their childhood, their education, etc.  Or characters who wrote backstories where they were an accomplished adventurer before the campaign began (the folk hero background exists for a reason), but had some in-narrative reason they were at a lower level (drink dulling their senses; becoming a fallen paladin and having to relearn their skills; etc.).

I have had players write a half dozen single spaced pages of backstory that did not place them in a position where their starting level did not make sense; I have had players provide a two sentence backstory that really did not fit with the starting level.  Length is not the important metric - content is. 

My answer is in my signature.

It's how the majority of the PHB handles it. "You are ______." "You did ______." "When ______ happens, you will ______ yourself."

There are some 1st person things in the PHB, though, particularly the background flaws, bonds, etc... (I'll edit them to be imperatives instead.)

I choose 3rd because it allows the reader of them to take some element of ambiguity from them and make them ask questions that I might have not thought about. Like currently I'm playing a Half Drow Paladin, back story is his father was a Drow who fled after (in self defense) he hurt a Drow woman, who came on to him in a way he wasn't comfortable with(keeping it pg-13 but yeah). He came to to the surface and was able to find love with an adventuring woman, they settled down and had my character. I have a name for my character's mother, in fact he uses exclusively his mother's last name (which is their family name with the father having abandoning his). And it's come up what she was because my character's eyes are a decidedly "weird for drow/half drow" color" and if I used first person I'd probably have described her as my character is always thinking of her and his father's final moments before being cut down by loyalist to the drow woman his father hurt.