Well, the easy answer is both.
However, since you might want a bit more than that...
The both versions use very similar mechanics, such that they are mostly indistinguishable. There are differences.
In the WWI version, you pick three maneuvers per turn, cycle through them, and them pick three new ones next turn. In the WWII version, you pick a new maneuver to put at the end of your stack of three after performing the first one. It's a subtle difference, but it really makes a difference in the feel of the game.
The WWII version also has a difference in speed, in that you can choose a slow or fast version of each maneuver.
They are both great, so I'd say you should pick the one whose history and aircraft you find most compelling!