Vision, G-tolerance or Health...

[Sky_Shark]

I prefer G-tolerance, the initial G tolerance in campaign modes is very low and criples your hability to dog fight properly. On the other hand, if you are the ground atack kind of guy, it's perfectly useless.

[Katahu]

For dog-fights, good g-tolerance is improtant.

For shooting out bombers out of the sky, health is needed since you're mostly attacked by the rear gunner.

And as for ground attack, you need good vision so that you can identify your bomb target sooner so that you won't bomb too late on the first run.