Some of these books are only a few months old.
Hopefully you evaluated based on better criteria than "They gave me a freeplay".
1. A heavy emphasis will be placed on speed of payments. Several books immediately pay out after the game has been graded. Those are the books with the least risk involved. Sweat the game, not the payout is not just a slogan. It should be a way of life for these bitcoin books. Bitcoin books have a much higher standard involved than post-up books because there are no fees involved and no need for a third party processor.
2. Grading time. Most postup books have automated grading; the winners and losers are determined minutes after the game is over. Bitcoin books that do this show that they have invested in their software. Books that rely on an individual to grade all games tend to have a high degree of risk.
3. Books not requiring personal information including an email address will be graded higher. Anonymity is a plus.
4. Date opened if less than 2 years. Bitcoin has just taken off in the past year, so it's unfair for one to compare a top bitcoin book with a post-up book like Pinnacle. But it is still important that a book shows itself to not be a flash in the pan. The longer a period of time a book has been open, the better its track record.
5. Limits. In general, the higher the limits, the deeper the bankroll of the sportsbook. If a bitcoin book takes high limits and pays out quickly, it shows its strength.
6. Sports and options offered. Uniqueness of lines and betting options is a positive.
7. Mobile betting. The ability to bet on the go can be important to some.
8. Live betting. The more, the better. Offering live betting isn't easy; the ones that do offer live betting lines tend to be stronger in general.
9. Customer service. The better the customer service, the more professional the book.
10. Interface. Ease of use is important.
11. Whether or not the book requires a deposit account. Depositing into a bitcoin book is a much bigger risk to the bettor, especially since these books have not built up a strong history that shows their staying ability.