Well... considering the really low startup of both of those Fairs, I'd imagine your reaction time would have to be extremely on-point to perform the move you want 100% of the time.
Well, since the recovery fAir is almost always
just used for recovery... Why not just make it so that you tap for the screw attack fAir and hold for the more vBrawl-ish fAir? Using the C-stick will use the tap version, so just use the C-stick for recovery and it works.
On a more present note, I feel that Samus' attacks are too laggy and don't flow into each other. For instance, her missiles start out slow enough that they're impossible
not to avoid. Here's an idea: Have her missiles start faster, and have them hit
backwards at a low-ish angle. This might sound strange, but think of all the combo starter potential of having a projectile that hits people towards you! Change her dTilt to something less... out there. Make it be a
huge explosion, but give it normal start-up lag and everything. Give her mines enormous explosions (between Bob-omb and Smart Bomb size) that are difficult to avoid. fTilt needs to be faster, for combos. fSmash needs either more range, more KB, more speed, or multiples of those. Maybe give her her old Melee Extended Homing Grapple Grab again? That thing was amazing (source: I'm a dedicated Spamus main in Melee, and I love mix-ups with it. Just make it quicker to activate, maybe a taunt...)