Mechanics. Pf2e is inherently tactical, and I like looking at a funky archetype or class feature and building around it. Backstory usually comes naturally when choosing what feats to take, and aesthetics usually result from that.

I'm curious to see how this correlates to the play style of people though. I come from the other side of the GM screen, and I think that's influenced how I build my characters.

I usually start with a very broad flavour concept, then figure out how to do it in mechanics, and use that to flesh out the details of the flavour.

There have been times when I’ve come up with a very detailed flavour first and then gone for mechanics later.

The only time I start with mechanics is with one-shots or other times I don’t particularly care about the character themselves.

I'll yield mechanics to aesthetics first, but I'll pretty much always start with mechanics as the foundation when i roll up a character. I'll ask what kind of character can spring up from someting like "Skeleton Barbarian," and stick with the idea more strongly than those mechanics.

I try and come up with something mechanically interesting and then work my character and backstory around that.

I usually start with a broad mechanical concept — melee, ranged, healer, or the like. Often that bit is discussed with other players to see what they’re thinking. I don’t want to end up with everyone trying to fit in the same niche on accident.

Then I refine the idea by thinking about flavor. Sometimes I’ll find a picture at this stage, then try to build a character around that. Otherwise, I’ll try to come up with an interesting backstory or bit of the world that we haven’t explored before and build around that.

Since I’m still relatively new to the system, it has to be flavor first, but that’s changing as i gain experience. My first char was (still is I guess) an Investigator and let me tell you, that is a tough class to start with. It breaks (in a good way) the fundamental “roll d20 to attack” mentality which threw off me, our new-to-PF GM, and the VTT.

My next was a Champion with Bastion (free) archetype, but I’ve ret-conned as I learn more rules to be Lastwall Sentry instead of Bastion. Champion and Bastion just had too much overlap- in other words the Champion alone satisfied my flavor-needs for protection and shield power.

I sort of go with both at the same time, I let the mechanics drive the flavor and flavor drive the mechanics. I usually come up with a concept first, then figure out the mechanics for it, and then further develop the flavor based on mechanics.

For example, my 5e pugilist character that focused on grappling and had a snake theme to her (snake tattoos and moves inspired by snakes like constrictors) was developed in PF2e as an Animal Instinct Barbarian (Snake) with Wrestler archetype for exactly the same flavor but more mechanics better suited for what I was looking for. I didn't want to go monk since the only snake-themed monk stance is more focused on Poison (Cobra Stance) which isn't what I wanted, plus she's more of a rough brawler type than mystical monk type.

I have to say, as a GM, I want the players to start with a concept and work from that. BUT I absolutely do not want them to start with a character from books or anime or some batshit crazy idea and expect me to beat the mechanics all out of shape to accommodate them.

I saw a post on another site (which shall not be named) where the player wanted to play a monk with eyes on the palms of his hands instead of on his face. He claimed it was for flavor but he also said he wanted to just be able to close his fists and ignore any negative effects from seeing something, such as a gorgon or basilisk. While I admire the creativity, I don’t have any interest in screwing up the playability for other characters and for myself.

When I’m a player I start with a role, then layer on something odd/quirky, then look at how I can implement it within the rules.

I go for mechanics. I'm not a huge flavor guy, but I get interested with mechanical concepts and want to see how it works out and if I can make favorable combinations. I haven't played enough 2e to know how well that works, but that's more or less what I've always done with TTRPGs.

Both!

What I love about Pathfinder character creation is that it doesn’t feel like either/or to me. In the games I was familiar with, there were usually only a few viable archetypes that would remain fun to play as you progressed through the levels.

Here, I don’t feel like you have to choose. Flavor supports mechanics which supports flavor back in turn. I’ve yet to come up with a concept that I couldn’t express with the normal character creation process, and I’ve never felt like there was a single “correct” build that I had to play if I didn’t want to be left behind by min/maxers at the table. I never would have seen it this way until I experienced, but crunchy tactical mechanics is the best thing that has ever happened to my role playing.