Las Vegas - definitely (my dd14 has a major crush on Greg).
Reasons why I hate Miami (the show, not the location):
1. Horatio's ridiculous one-liners.
2. Investigators spotting miniscule pieces of evidence across the room while standing in the open doorway of a dark room.
3. The co-star investigators have NO personality.
4. The grim, angry look on everyone's face - they take themselves way too seriously.
Las Vegas has comedy, personality, inside stories, as well as the fascination of it being the First CSI.