Audio books are generally one narrator.
Audio plays are ensembles. I love my hobbit radio play. Lots of actors, narrator and music as well it really is fab and one of the main reasons I still insist on tape players.
I like Stephen Fry's voice (if not HP books themselves).
Tony Robinson is outstanding for the disc world books, my only gripe is that they are abridged.
I got given the complete hobbit and Lord of the rings unabridged audio book a few years ago and it is wonderful on many levels.
I listen to lots due to using them as crutches to sleep, but miss being able to trial a bit in the bookshop. I also refuse to use audible as I need them on cd.
Some are very expensive to buy without being able to hear a sample.
I think I prefer male voices over female, except for things like Austen. There's a very good one (available on youtube) of her P&P that was made for librevox in '07.
ETA: the guy that reads the Darren Shan demon stealing series (present from a friend who knows I like comic horror type stuff and audiobooks) is amazing. Perfect choice for the books I must say (which aren't amazing but the audio versions are topclass) and he uses a crazy variety of voices. No good for going to sleep though, the voices are too different and distinctive.