A direct comparison of Kirby and Pichu, just to help settle the "who's worse" debate:
Survival: Pichu's recovery is good, but the vulnerability and self-damage are annoying. Kirby's is nothing to sneeze at, but it's still easy to intercept, and final cutter is just lol. As for weight, Pichu is of course, lightest, but Kirby isn't much heavier.
Approach: Pichu really has only nair SHFFL. Tjolts are ok for occasional pressure, but they really should be kept to a minimum. Kirby has bair, which is actually a relatively good move, and fair, which sometimes works as well. Kirby is slow both on land and in air, and Pichu is reasonably fast in both areas.
KOs: Pichu has a fairly strong usmash, but the cooldown is punishable and as with all Pichu moves, lacks range. Fsmash is very strong, but the range is lol and people can DI out before the last hit. The weird knockback on dsmash can fool some people the first time but it's not very reliable. Nair can KO at high %s. Pichu can gimp with nair and fair against some characters. On the side of Kirby, he has his uair, which KOs 130-140ish? He has bair offstage and dair gimps, and the infamous Kirbycide(situational but can really turn the tide of a match).
Camping/Defense: Kirby can hide behind bair in some cases. Pichu can't really camp at all. Both have small shields and small grabs, but Kirby has a little larger of each. Pichu has a short tech roll and roll dodge, making it harder for him to get away from an aggressor.
Punishment: Kirby has grab combos and u-tilt chains. Pichu has a few grab combos and uair juggles. Not much to say here.
Overall, it seems that although Pichu is faster and stronger, Kirby is a "safer" character who doesn't need to be as careful as Pichu, as well as both punishing and avoiding punishment better.
...Poor Pichu might actually be the worst.
But he still has the best taunts.