I didn't beat the game yet, so I don't have the option to use Ultima

Counterpoint, Divewing, Sweet Dreams or Unbound.

Uhh, the strongest keyblade?

 

At this point, you should at least have Divewing. It's not very hard to get, and I recommend going for it if you haven't already. End of Pain is a really good one, but it takes forever to obtain, so you probably want to scratch that one out. The "best" Keyblade in the game is Unbound, but you have to go through a lot of bosses to get it. And let's face it, if you actually managed to complete the insane boss run needed to get Unbound, you have absolutely nothing to worry about going up against Young Xehanort. But for now, the Keyblade you get from clearing Sorcerer's Symphony should be just fine.

Divewing. you should have it by the time you face him

the key bladeshouldnt be your main focus try using alot of balloonga and curaga

Use Way to the Dawn. Kickin' butt like a boss!

Steal his keyblade and go ham on him

Way to Dawn. It feels right to use the default keyblade.

If you don't have Ultima Weapon, then I recommend Unbound.

Well it depends if you're more of a magic or physical attack person, but who ever plays these games and goes to be strong in magic? Hahaha Counterpoint is what I used for a long time, but go for the Unbound by doing all special portals, or Divewing, I guess.

Hurrmmm...well the only Keyblade I've used against him was the one you receive after finishing the Symphony of Sorcery (think that's what it's called) world. That one worked fine for me.

Well, you can't get Unbound and Ultima until after beating YX a first time, so i recommend Divewing or End of Pain, as those are the strongest keyblades that you can get before the final boss.