I think justdice, as it is a long-standing gambling website. The only problem is that they use an alt-coin called "clams". These are sometimes considered scam-coins as a few people own the majority of these.
Why do not they use other coins? One reason could be that they are supporter of Clam and Clam is a PoS coin. When user deposit Clams there, Justdice will earn interest with the coins.