For me it's a no-brainer: Crypto-Games
Why? Well, first and foremost they've supported me on this forum since 2015 through their signature campaign.
Okay, you might think that makes me a little bit biased and you're probably correct. That said, I actually do also like to gamble there.
They've been active here on Bitcointalk for several years, haven't got a single
trustworthy negative review and their website is generally very pleasant to use.
Why would I switch to another website? Crypto-games supports most of the major altcoins and Bitcoin and they offer near instant withdraws.
Deposits are added after just 1 confirmation.
They also have a lot of promotions, always
without rollover requirements.
Their chat on the Crypto-Games website actually has some decent discussion going on. Their rules are stricter than on other gambling websites, but it hugely improves the quality of conversation. Big fan of that!
Also, at 0.8% house edge, it just makes sense to play dice there. Haven't seen too many websites that have a lower house-edge.
And their games are fast, simple graphics make for fast games.
That's about it really