Pure rules or homebrew?

Are you more of a fan of pure 5e rules, or do you regularly tweak your own Homebrew for campaign balance?

I usually tweak. Though it isn't always for campaign balance, it is sometimes ease of play, i just want to add something cool, or I have to rebuild something from an older edition so a player can use an older character in 5 or 5.5. 

I tend to tweak things that I find lackluster about the base rules.  Things like the rest balance (both the base and optional rules I find do not hit the nail on the head for my groups), resurrection magic, and a few other minor aspects of the game that feel a bit half-baked.

Which, I should note, is exactly what the game designers set out to do with the rules, and have since the very first edition of this game.  I don’t think I’ve ever played in any group, in any edition, where there was not some degree of homebrew to better make the game line up with the party’s playstyles.

Granted, one does have to be careful with homebrew that you are not transforming the game so much it is no longer recognizable as the game folks chose to play, or to implement homebrew that makes the game less fun (things being unfairly over/underpowered, targeting certain players with nerfs, allowing players to step on others’ toes).  Lots of ways homebrew can go wrong, so it is important to be willing to rebalance and talk with players about what works or does not.

I tend to use the actual core rules as written/intended, though, unless a rule doesn't make sense.

Flight rules are one such case where I unintentionally & subconsciously balanced them by saying that a flier needed to land/be supported after expending their flight speed & couldn't just stay aloft, and hovering meant literal hovering.

As for homebrew/3pp...I find that above-table talk tends to clear the air with a lot of overpowered/underpowered white room scenarios, and consent checklists help with elements someone isn't cool with.

I allow most 3pp as long as it's fun for everyone at the table & it's been cleared by me...once, I had to nope Torture Ranger(Someone brought a 2014 ranger using DND Beyond Homebrew with what would turn out to be the Steinhardt's Guide version) because of a different player having most of that subclass's flavor & mechanics marked as red on their consent checklist. The Ranger player had this clearly explained to him, & he understood completely, choosing to play a Green Reaper instead.

As much as possible I play straight 5.5e rules but I do sprinkle in a few of the old 5e rules that I just prefer (like the Lucky Feat still being useable after you’ve seen the results of the role instead of just giving advantage, a sorcerer twin spell still actually twinning instead of upcasting, and the Druid wildshape using a monster’s HP instead of giving temp HP) As for 3rd party stuff I’m fairly permissive, basically anything on D&D Beyond that I’ve bought is open to my players and anything else would probably be allowed so long as they did the hard work on the homebrew 

I use core rules and a few houserules.

I routinely homebrew monsters and items, but I'm not sure that's what the OP was intending. I have a few house rules, but I try to keep the list limited.

I distinguish between houserules and homebrew; for me, houserules are changing the way something in the rules works, while homebrew is creating something that doesn't exist or that the rules don't cover. We stick to RAW wherever possible, but when it comes to these two deviations, we lean more towards the former than the latter. 

A common houserule we use is the somatic/material components thing - we allow a hand holding a spell focus (or something that counts as a spell focus, like a pact weapon) to count as "free" for somatic components no matter what. In the RAW, that only works with spells that have both a somatic and a material component (which is why it always works for Artificers, since all of their spells have a material component.) WotC had a chance to streamline this functionality in 5.5 but for whatever reason they didn't, so we did it ourselves.

I homebrew adventures, treasure, monster, background, race etc in many case bringing older game element to 5E but sometimes stuff of my own invention as well.

a little of both, generally at the start of a new campaign as DM we do a session 0 and work out which rules we use. 

They end up being mostly by the book rules with all classes, species, and feats from a set list of sources. I add in a few minor homebrew rules like flanking for advantage, and cinematic use of hero points. 

I also remove the concentration requirement on hunters mark at level 7, and make it easier for rogues to get backstabs.