Well, I've played on a bunch of sites and honestly they are around the same with respect to their reputation.

I think that you can't really go wrong with either Nitrogen, Betcoin.ag, or Stake. They have all been around for a long time and have paid out huge winnings without any issues (and their betslip grading are generally all quite fast as well).

As long as you avoid the known suspects such as Cloudbet, or others who tend to hold user funds regularly for KYC purposes, you will be fine.