That's a tricky one...since I quite like a lot of the characters.
In the first movie...I'd have to say I'm not too much a fan of Timon. Don't get me wrong, he's funny and all. But the way he take's advantage of Pumbaa's slow wits is...
In Simba's Pride, I'd have to say I find Nuka rather annoying.
As for Lion King 1.5...I've only watched that once, so I can't really form any opinions there.
Like I said, I like a lot a lot of the characters...this is a more a matter of which ones I like the LEAST, rather than which ones I hate.