Okay, to be honest I don't know which characters are 'better', but my favourite is Scorpion, Sub-Zero and I'm quite fond of Frost. At first Frost annoyed me, but she's like one of the only female characters I like playing. I guess I also like Kitana, but still would prefer Frost. Oh, and I think my reasons for liking Scorpion and Sub-Zero are fairly obvious. Well, that is, I like them when they aren't beating me. Sub-Zero isn't really a problem, but Scorpion was a bit of a problem in Konquest. And a even bigger problem when I versed him on Arcade on hard. But I totally owned Arcade with Scorpion.
... I'll never forgive Noob for beating me during the Konquest mode. It was, like, the first time I'd played Mortal Kombat in years, so I was still getting the hang of things, and this Noob character showed up and totally owned me. It really sucked because he was called Noob - and I had to try and explain to my mother (who was getting concerned) who was beating me. I was thinking there was no way Noob could be a serious character! Not with that name.
And I absolutely HATE Mavado. Hate him. With a passion. I can't really explain it - but I hate him. He's just... annoying. And for some reason I really don't like Ermac. Maybe I just haven't quite masted him yet, but I don't like him anymore. I tried being him in the arcade - which I set on NOVICE while I played around with him. Psh, he sucked. He really did.