Been around doing this for quite some time. Just felt it necessary to express my opinion of good sportsbooks for USA clients.
1.) 5dimes - for me they are #1 because of their extensive betting options. You can also parlay just about anything together including props of different games. Deposit options are fantastic if you are a long-term client. Payouts are fast, on time, and cheap.
2.) Heritage - great customer service by far compared to other books. They are very close to #1 but not quite due to the fact they do not allow you to parlay random things together. However, they do carry some random lines in soccer or european hockey that 5dimes does not cover which I enjoy.
3.) Youwager - surprisingly awesome customer service, maybe the best in my experience. Lacking wagering options as well as slightly more juice on props/live wagering/totals than other books. You can withdraw winnings while rolling over bonuses which is awesome. This book should be higher than its B rating, perhaps B+ or A-.
4.) BETDSI>bookmaker>justbet - great for high limits and being ultimately trustworthy. Lack of parlay options and open parlay doesn't work for me. Payouts can be expensive.
Books that are rated way higher than they should be:
Betonline - I have not had any bad experiences exactly but they just give you the shady book vibe. They did payout a fairly large amount but took much longer than stated and me hassling them to get it done.
sportsbetting.ag - Not very customer oriented at all. Their live chat takes forever to have a conversation as they are slow to respond. Bonuses require 30 day wait for payout even if your rollover has been met. Never taken a payout from them but everything across the message boards say they do payout but just takes much longer than stated.
These are just my experiences. Everyone's experience will be slightly different. Hopefully this will help a few people along the way.