Uair: Wario's is faster and kills pretty darn good. It can also juggle Kirby if he isn't on his toes. Uair for Wario has surprising priority, it might even have more than Kirby's.
Again, Kirby really shouldn't be getting juggled by up airs. Kirby can fly and if Wario is approaching Kirby in the air, Kirby should be able to react by spacing with back airs and such. I just really don't see Wario juggling Kirby with up airs.
They might be about the same speed on the ground, but it is certainly clear that Wario is more powerful.
Actually, it really isn't clear that Wario is more powerful on the ground. The only move that can KO outside of smashes on the ground is a forward tilt, so that might be a slight advantage over Kirby. Besides that, let's compare the smash attacks.
Forward smash: Comparing both the KO powers and the weights of each character, both forward smash from either character will KO at about the same percentage. (Yes I am saying that Kirby's forward smash is a bit stronger)
Down smash: Kirby's down smash will kill Wario at about 120%, as will Wario's (talking about non staled here). Kirby's down smash is stronger than Wario's while Kirby is lighter.
Up Smash: It's pretty clear that Kirby's up smash is overall stronger, killing Wario at about 115%, but Wario can go farther with his. Wario's up smash is more for damage dealing anyways.
So to me, it doesn't seem that Wario is not that much stronger on the ground, if any.
Yes, I am almost certain Wario's is stronger than Kirby's, go test them both on a Mario at the center of FD and you will see that Wario kills him sooner than Kirby does (can't test it myself right now).
Again, I believe Kirby's forward smash has more KO power than Wario's. But comparing the two weights together, they will KO each other at about the same percentage. Here's a video of Kirby's forward smash killing Snake at a little over 100%, at about 41 seconds into the video.
http://www.youtube.com/watch?v=yP6T3wEH5Pw
Kirby's ability to recover successfully most of the time is nullified by the fact that he will more than likely be dying somewhat quickly. What good is it to have an awesome recovery if you are dying before you reach 90-100% damage every time?
The only character that CONSTANTLY kills me at 90%-100% is Snake. It's very rare for a Wario to kill me that early. I'm assuming you're talking about a forward smash here? If so, they first would have to never use their forward smash before that percentage (from what I see a lot of Wario's don't do that, correct me if I'm wrong) and they would have to pull it off on me. We're talking about a move with bad after lag.
You could probably kill Kirby at 100% with an up air as well, but as I said before, Kirby can fly and a good player should see the move coming since Wario has to get so high just to hit Kirby. You shouldn't be able to pull off an up air close to the ground either because Kirby can space himself extremely well in the air with back airs.
All in all, looking back at both of our comments, it seems that Kirby can KO better on the ground while Wario can KO better in the air.