Hard to cut it down to 1 out only, but I think the following books are deserving of a mention:
Pinnacle, the best prices out there (10cent line). Although, I must admit a newbee can only cash if he catches a good luck streak.
Hollywood, good lines at -107 or a 14 cent line. I have been able to find a couple of "best prices" various times. And they pay like clockwork.
CRIS, gotta love those openers. We'll see how they do now that Mac is not there. I think this shop is the biggest book out there.
VIP, if you are a small player. If you want to grind them pebbles, go somewhere else... they do not book arbitrage plays.
5Dimes... simply put, Tony is out of his fvcking mind and he's one of the shrewdest bookers/players I ever met.
I personally like Cascade. Lenny is a good sharp guy and he's got seriously BIG back-up these days. I'm looking forward to seeing those numbers during NFL.
Also Grande, WWTS and betIIS.com
Just my .02