Fair is a nice combo move, and works to hit people in front of you when you're airborne (duh) You can fastfall it before the final hit to chain it into some ground moves like dtilt, ftilt, dsmash, or maybe even Usmash if you're lucky. It's a good approach, too.
Bair is priority central, and does some nice damage. Some people also think you may be able to gimp people with crappy recoveries by dragging them offstage with this. It can only be done laglessly if you full hop it.
Uair is combo city! You can chain uair into uair into uair over and over again, and finish it off with a Nair if you'd like. It has low knockback, so it's perfect for this. Oh, and the semispike at the tip of the tail is gone, sadly. ;-;
Dair is nice, but is usually people's least-used aerial for some reason. It does 12%, which is VERY nice, in one hit (so no SDI out of Bair or Fair), and has a nice knockback angle (almost a semi-spike) with some pretty respectable knockback. I think the fact that it auto-fastfalls if used not during a jump (many people c-stick their aerials) is a bit of a turn-off, despite it's excellent potential to be a great gimper. Also, it has a TON of priority, and can be autocanceled by short-hopping and doing the Dair right as you leave the ground, which makes it a potentially AWESOME approach! :D Also, you can QAC directly into the landing hit of this for 4% and some okay knockback. It's the only aerial that can be done this way.
Nair is probably Pikachu's best aerial. It may not have a ton of priority, but it's FAST FAST FAST. It's nearly instant to come out (which makes it great to use as a finisher to a Uair juggle), and is a sex kick. If you hit on the first frame (you gotta be super close and right next to them basically as you press the button), you'll get LOTS of knockback! I'm talking KO potential, folks! I forgot how much damage it does, but it's pretty respectable. Even if you hit with the weak hit, you still have enough knockback in it to probably gimp or get away before they can hit you back. It's also an incredible move to perform out of the QAC ( and is probably the best aerial to QAC into). Also, because of its INCREDIBLE knockback, it's a very good move to edgeguard with!
