There is a nice writeup on primagames that explains the difference:
One of the more dependable vehicles you'll find in Fighter Squadron, Walker Assault or Supremacy, the A-Wing can deliver a great deal of damage, while at the same time generating a temporary shield to protect from damage.
Locking on to enemies with the A-Wing is a snap by holding down the left trigger. From there, you can fire away with your blasters (if they're not overheated) and shoot concussion missiles once they lock on. Both of these do significant damage, but make sure you protect your backside, as an enemy is likely to lock onto you.
Evasive maneuvers can make all the difference as you can barrel roll or execute a 180-degree turn to get out of harm's way, and perhaps even get the jump on your opponents. You can also distribute your speed by pressing either up to shift the power to your engines, or down if you want to cycle to your weapons.
The X-Wing is similar to the A-Wing in terms of the weapons provided, including shield and lock-on proton torpedoes, but it has a better firing range thanks to its foils, and a little better maneuverability on tight turns.
Again, the lock-on and evasive techniques remain in place as they did before, so be sure to get every fighter you can, while at the same time protecting your own hide. The same energy distribution system is in play, so whether you need speed or firing capability, you can switch to both with relative ease.
The Dark Side is strong with this vehicle, as TIE Fighters can lock onto enemies as well, firing lasers and the Ion Cannon to deliver a devastating blow. For good measure, you can also use a speed boost if you feel like rushing into battle or getting away from a particularly crafty enemy.
As with the Rebel vehicles, TIE Fighters also have energy distribution, so you can balance what kind of firepower or speed you need with your vehicle with simple nudges.
One more thing – the TIE Fighters have great maneuverability in the air, but can take less damage than X-Wings. Keep this in mind the next time you get into a dogfight.
Finally, the TIE Interceptor is a slightly more advanced version of the TIE Fighter, with most of the same abilities and handling we've come to expect. If you prefer to pilot something to what Darth Vader handled in the first movie, this is the best way to go.
You'll want to make proper use of its energy distribution and keep an eye on your six in case you need to do a quick barrel roll or 180 spin. Remember, it’s just as vulnerable as the TIE Fighter, so you'll want to whirl around and get back at your enemies with gunfire as much as possible.