I wrote up some solid reviews a couple pages back so i'll weigh in.  I think most of the ratings here are decent based on the "time" criteria.  I do think cloudbet might be the best right now, but if you cap what a book can achieve based on time in existence than cloudbet is where it should be.

however, that being said, JUST because a book is the oldest (anonibet) doesn't mean it should be rated the highest.  the review i posted about anonibet and several others here are pretty scathing when you subtract out the fact that they've been open the longest.  they are pretty much the worst across the board on 5 other criteria points.  frankly the book itself is D+ to C- at best when you take EVERYTHING into consideration (other than time open).  i DO think that other peoples complaints about anonibet are legit and it should be downgraded considerably because all aspects of that book suck other than the fact that they've been in business the longest.

there is one other thing to consider though.  i think anyone can open up a bitcoin book like anonibet with roughly 50 bitcoins in cold storage.  the fact is that the average bettor probably wagers .05 BTC and so when anonibet caps action about as low as possible there is almost 0 risk to them as far as someone like me ever winning big.  i would be shocked if they could release a cold storage wallet address proving they had 500-1000 bitcoins to back their book.

I would rather play at a brand spanking new book who released a signed wallet transaction showing good backing (1000 btc) then a lowly capped book like anonibet that prays off people who are zero risk to them (especially when their posted odds are so terrible they they gain a extra 10% handicap advantage over all the other books).