In my opinion, Kovu was never "bad" or evil to begin with.
But in answer to your question: It’s pretty much a tie for me. I like "bad" Kovu because it makes his personality match his looks, if you know what I mean.
He is more sarcastic, and just seems generally stronger..
I do also like good Kovu because he is gentle, kind, romantic, cute, and, well.. sexy.
When it comes to choosing one, I voted for Good Kovu.