Worst: Kira's. I mean, all that only to get taken out by a third rate Ken Master's clone? Bull.
Best: Liu Kang or Johnny Cage.
Actually, add Scorpion, too, because I always hated Quan Chi, and if old Skull Dragon got that power, Quan Chi would get taken out sooner than later.
The later for the fact that Johnny experiences character developement. Also, he does not deserve half the flack he gets, especially since there are so many more characters that are actually bad. I didn't like the MK4 version of him, but I generally don't like MK4 anyways.
Use him on VS mode in Shaolin Monks; not bad at all.
Now Liu Kang's is my favorite because not only does he get restored fully, but he becomes powerful enough to take down Raiden. The ending itself reminds me of something that has the feeling of the older MK games.
One more note: Blaze was a pushover; they should have made Raiden more powerful and had him as the final boss, considering that he was now corrupted, ruthless, and obsessed with protecting Earth at any cost.