Hey Rick,
Leno is right, look for how solid the book is as your first priority. I've lost well over 1500.00 with one book folding on me, another suddenly reducing my account by 280.00 after a server crash and I narrowly avoided going down with Aces Gold, taking a sizable withdrawal a few weeks before they folded.
This site has a lot of great info, but I go to Sportbookreview.com to make my decisions on books. He doesn't take advertising money, updates any book that's slow paying or changing lines and rates several hundred. I wouldn't go with anyone he rates less than a B-.
Rog