I think the appeal of Trevor is that he's every spontaneous rampage, hooker beating, pushing people downstairs and generally terrorizing everyday citizens all rolled into one angry package. I've always preferred to play in-character, so when it comes to doing anything outlandish as say, Niko or Luis, it never really fit. Character's like Tommy Vercetti or Johnny Klebitz I think it worked better for, but still not completely. With Trevor, from a role playing perspective anyway, it feels like you could throw your violent toys around for no other reason than he's having one of those days.
Micheal definitely has the most compelling story so far and seems to be the lead, probably the deepest of the three characters as well. I feel like while his story will be the most interesting, Trevor will be the most fun to goof around with. Franklin is kind of a mystery right now...?
EDIT: That could easily be the McFarlane's home after 100 years of renovations, but I never got the feeling RDR was set in California. More Texas, Arizona or Montana?