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.
Clam is the most held coin in crypt-currency history. Fairly distributed.
Like this many people now a days prefer alt coins to make dice gaming or any other gambling just not willing to risk their bitcoin. This will not letting out bitcoin from gambling industry.