My experience only, of course, with these 2 top books.....
*Customer Service: I found both to be fairly quick to respond to emails and both quite competent. Scotty at Betjamaica is one of the best in the industry, as I have found from personal interaction. Conversely, Tony at 5Dimes has a reputation as the AntiChrist of the wagering world, though to be fair I've never had to deal with him directly so I can only relay what I've heard. Other reps there seem more than adequate.
*Payout: I've only ever used Neteller and Moneybookers, and payouts from both shops were quite quick, always the same day and within a few hours. 5Dimes somewhat quicker, but the difference is negligible.
I might also add that both will put limits upon you. 5Dimes will also put you on a delay if you are beating them, then a further delay and in my case, will outright ban you completely if need be. BetJamaica moves from a 10 to 25 second delay, but as far as I can tell will never actually give you the Red card. Curiously, BJam has no delay on props betting, but will slash your limits (I'm maxed at $100 clear across the board for props).
One man's experience but hope it offers some perspective.
IMO, Bet Jam all the way as far as payouts go. Customer service is #1, there are a lot of US companies who could take a lesson from them as far as being polite on the phone goes.
For the average, recreational bettor I would choose BetJM hands down... But if you are looking for alternative lines, teasers, and all that other stuff, you gotta go with 5er..
For withdrawals both send checks to Canada, so thats a plus, but for wire 5Dime is better cuz you don't pay nothing 1 free per Calendar month, but at BetJam you get 1 Per month too but it doesn't cover for Bank Wires, thats kinda sucks.