I think it's important to note, as pointed out in the edited OP, that this poll is only concerning itself with the question of "What do you do in one specific instance of play at the table?"
I.e., it's your turn and you can choose to do something that's tactically advantageous (providing you with some sort of mechanical advantage) but out-of-character for your character, or to do something that would narratively fit your character's personality and decision-making process, but doesn't provide any mechanical advantage or puts you at a disadvantage.
That's an entirely different animal than just the general philosophical dilemma of narrative vs. numbers...
For myself, I generally try to find the best balance between the two that I can find in that particular situation.
Most of the time, if the most tactically or mechanically advantageous action to take in a particular situation isn't that far off of whatever choice my character might make without mechanical considerations, then I can generally come up with a narrative reason for them to do it.
I tend to play characters that are both reasonably intelligent and fairly pragmatic, so it's usually within character for them to analyze the situation at hand and try to resolve it as efficiently and smartly as possible, and hopefully find a way to work it out to their advantage. They generally follow the philosophy of: "There's Good, there's Bad, and then there's Necessary...", so if they're smart enough or wise enough to realize in that moment that taking an action different than what they might otherwise be inclined to do might be better for them, that's generally the action they'll take.
If the mechanically advantageous thing to do is wildly out of character, then it becomes a matter of determining if the stakes involved warrant the character making that kind of decision in the heat of the moment, or at least being willing to go along with that sort of action. If it's a matter of hitting a party member with your fireball just to get a few more mooks inside the radius, that's probably not worth the narrative betrayal of the character's principles - assuming the character has them, lol. Which is an entirely different level of moral/philosophical decision than having your shining-knight LG paladin suddenly choose expediency over morality and bullrush the skinny mage BBEG off a balcony in the final battle of the entire campaign instead of fighting him fairly.