I also voted for "I try to be the character" since it's the closest fit.
What I actually do is this:
First, I think about what my character would do.
Second, I try to think about what would be best for advancing the story.
Then I try to coincide one with the other
Back in the days I would act out what my character would do - to hell with the consequences and the DM's plans!
This, for me, too. But I don't think, "I try to be the character" is the best fit. I think that way lies madness.
Characters are fickle things, and tend to do annoying things like rebel against storylines, leader-types, authority-figures, and any and all established guidelines. Players - and I include a younger version of me! - who hold "it's what the character would do" up as some sort of aegis against accusations of being a ... game-disruptive person ... are mistaken.
The character exists as an implement, a tool to be wielded in tandem by you the player and your Storyteller, to arrange for everyone around the table to have a good time. To allow your tool to rule you is folly bordering on lunacy.
I think the maturation from seeing the character as a gamepiece, with no more attachment than the shoe in Monopoly, to a being in their own right, fleshed out and with desire that sometimes (often!) run counter to creator and game intent, and finally, to an implement through which to put the creative enterprise you're engaged in into motion is a natural progression for most (not all) gamers. I've seen it in myself, and along stages in every gamer I've ever gamed with.
Not that I'm saying other styles are 'wrong'. They're <exactly> right - if that's what you're doing, right now, and it works for you. Just that, in my experience, the best gaming comes from a group that sees characters-as-characters-who-are-also-just-gamepieces.