Miller seems to be a bit more passionate about fighting. You wouldn't expect it from a guy like him but he is definitely a very knowledgeable person who is exceptional at breaking moves down. He's also a more relaxed guy who is known for his great sense of humor and it seems so far that he is extremely loyal towards his fighters. Definitely the qualities of a great coach.
Bisping on the other hand has his favorites that it seems like he puts more work into. Also, his rash shouting and demeaning personality is exactly what a coach SHOULDN'T be like.
It's a no brainer. Miller all the way.