My experience so far:
BRU RAY
+ better audio
+ bigger selection of movies overall
- movies generally more expensive (fuck you Fox)
- special features aren't very special
HD-DVD
+ more diverse catalog titles
+ more interactive special features
- nothing's really coming out after the holidays
- no lossless audio EDIT: Lossless but doesn't sound as good to me
PQ is a wash. They both look great to me.
Next purchases are Adventures of Robin Hood, Casablanca, and maybe the That's Entertainment! box set if they remastered all the clips