There are 100 other threads which are dedicated to the same purpose as this one.It would be great if you can just lock this thread and dig deeper for those threads.Everyone would applaud the websites they have in their signature as "the best" one which is not true in all the cases.

Crypto-games.net
PrimceDice
BitDice
are a few good names that have been around for a while.Crypto-games.net provides the best gambling experience and accepts a variety of alt-coins. (At this point you may want to click the link in my signature)

Websites to avoid (based on personal experience)
betcoin.ag
luckygames.io
bitcasinio.io
vegascasino.io