I'd say the best malks I've seen are ones who have chosen a suitable mental disorder and played a character with a mental disorder. Not a character who is 'insane'. I've had great fun playing a sociopath having first spent some time picking Martin's brain on what the disorder actually meant. I then played a newly-embraced and rather lost sociopath, and it was quite interesting.

Then I got blown up by a Tremere infernalist, but that's another story.