About to finish my first 5e Full campaign. Rise of Tiamat. Been playing for a year with my friends. I have some ideas for a new character, but I’d like to hear some cool ones that are fun to play.

Variant Human Vengeance Paladin

Forest Gnome Arcane Trickster

Variant Human Dragon Sorcerer

Tabaxi Bard. 
What do you think would be fun in terms of combat and RP?

Happily accepting other ideas as well. I didn’t enjoy my Monk that much throughout the whole campaign (not dms fault) for some reason. Still fun but looking for something that would be really fun to play.

Best will vary wildly by player.

What do you want to be able to do in combat?

• control the battlefield
• hit like a truck
• take lots of hits
• fling spells

What do you want to be able to do while exploring or in a social situation?

• sneak around
• be good at noticing things
• be really scary
• can charm anyone
• talk to animals

They're all solid options for all three pillars of play. No-one can tell you what you'd enjoy playing, but you need to like your character first and worry about the mechanics second. Unless the mechanics annoy you, in which case you picked the wrong class...

I’d like to hit like a truck and fling debuff spells. Out fo combat I enjoy finding things, problem solving, and sneaking around. Mostly problem solving and finding things.

Given that description, I think Arcane Trickster would fit. With Sneak Attack you will deal a lot of damage, and with access to the Enchantment and Illusion spell lists, debuffs shouldn't be a problem.

And then the rest of the rogue kit perfectly fits finding things and problem solving.

Forest Gnome Arcane trickster seems to be what you're looking for!  Hits pretty hard with Sneak Attacks, has some solid debuff spell options.  At level 9 when you're hidden you can even force targets to have disadvantage to saving throws which is pretty neat.  Obviously a very sneaky class.  Finding things and problem solving tend to be skill check related, often investigation which is Intelligence based.  Sounds like you'll love it!

Looking at Revised Ranger. Especially gloomstalker. This seems fun. 

As a note about the revised ranger, it is no longer considered active content. The gloomstalker was published in Xanathar's Guide to Everything.

If your DM allows homebrew, the group I play with has our own Revised Ranger that has been used in a few different games by different people and works well without being OP.

https://docs.google.com/presentation/d/1aebOM6u7XBNDLcJkXrNnh1BvuPJ9llPxA81nULlysxw/edit?usp=sharing

Quote from Houligan >>

As a note about the revised ranger, it is no longer considered active content. The gloomstalker was published in Xanathar's Guide to Everything.

If your DM allows homebrew, the group I play with has our own Revised Ranger that has been used in a few different games by different people and works well without being OP.

https://docs.google.com/presentation/d/1aebOM6u7XBNDLcJkXrNnh1BvuPJ9llPxA81nULlysxw/edit?usp=sharing

 Okay. I’ll check it out.

I like it a lot. I’m going to home brew in the gloomstalker if that’s fine because even if it’s more op I’m not too fond of the beast master. Mind if I use it?

Yeah, just put gloomstalker in as is. I had to adjust beastmaster because its not good where the official one is.

The subclass features are gained at the same levels, the homebrew is just to replace base ranger and the beastmaster. The XGTE subclasses are usable without any further adjustment.

I think the ones that are best to play are the ones you accidentally stumble upon and then spend the next couple days day-dreaming about the character.

Mechanically, it's all up to personal taste, but I think the characters I really enjoy playing are the ones who I look forward to spending time with. That's a tautology. But I will be the stick in the mud to remind everyone that mechanics are just a vehicle to story telling and D&D boiled down to its tactical simulation would be a really boring game.

In terms of making interesting characters, I think really the easiest way of facilitating that is to create conflict within the character's design: a divine soul sorcerer, of evil divinity, who refuses to be evil just because his soul is, for example. It would be easy to take that character and make them evil with an evil soul, but having that conflict between the person and this condition that is, more or less, forced upon them makes for an interesting character-- and interesting characters more or less write themselves.

Additionally, flaws can make for some really compelling characters. Low ability scores (try to avoid intelligence, as a general rule. Everyone has an idea of how to play low int, but in my experience not many people can do it well) can be a great jumping off point for a really compelling character. Don't play this broad: low CHA played as a jerk is really boring and stops you from engaging with the world-- often.

That's my take on the "best" character concept. I'm sure plenty of people can tell you how to make an evoker with shaped fireballs that can hurt people immune to fire.