I personally prefer dogecoin and ethereum but these days ethereum also have network congestion and fee is really high so dogecoin is best right now.
Raiblocks is another coin that have no confirmation time and zero fee and I think it will be accepted in some casino soon because nobody wants to wait for hours to get confirmation and pay high fees just to move coins in and out of the casino.
What other coins you guys think can be viable option for crypto based casinos?
I think every crypto casino that wants to be up to date has to support multiple coins to cover all the possible needs of their players. Here's my list of coins that I would add if I was running a casino:
Bitcoin: the king of crypto, still very popular even despite high fees, and Lightning Network is coming closer and closer to mainnet release. Also, Bitcoin is the best coin for bankroll investors because it's less volatile and more predictable than any altcoin.
LTC: Bitcoin's younger brother, currently has cheaper fees. Potential for atomic swaps and Lightning.
Dogecoin: ultra cheap fees, perfect for players with tiny bankrolls.
Monero: the best privacy coin, very much needed in online gambling for some users.