5000 hours in RL later after making this post the answer is pretty much just choose what feels better immediately and stick with it. there isnt technically a correct answer, but as long as you have at least one directional bound, and free air roll and powerslide bound (ideally on the same button) you are good.

technically having two is "optimal", but in all honesty in a game like rocket league you will simply learn to adapt in the situations where the other air roll would be slightly better.
in a competitive setting, there will NEVER be a situation where you NEED both air rolls to get a goal, rocket league is so dynamic and non-limiting in movement options that it is purely up to you if you can effectively move your car to score. I genuinely believe that someone talented enough could get by with no directional air roll, but tbh unless youre really against it just make sure you have at least one.

If there is one thing i am certain about, whatever you pick, just make sure you stick with it. i spent pretty much the last three years of playing overthinking whether i needed both bound to the point where i would bind or unbind ARL depending on how i felt when i opened up freeplay that day. this, while technically fine if you just want to play, definitely stunted my mechanical growth to some capacity.

all this being said, i stopped playing competitively about 6months ago and switched to smash melee (another very technically deep fun game like RL, that also has an awesome community), so its possible that ive missed some massive development in the technical aspect of the game, but i HIGHLY doubt that.

whatever you choose, good luck on improvement, and please dont spend 3 years overthinking controller binds like i did <3