I actually prefer altcoins these days, for two reasons. Firstly altcoins are easier to gamble and cheaper as well, when you gamble with 2 dogecoins you are not risking too much money and its much more fun, you have to bet with like 100 satoshi if you want to not risk too much bitcoins and that doesn't feel that comfortable, however I can gamble with many 100 litoshi and I could be gambling basically nothing at all and still have fun, so the price plays a big point in picking alts over btc.
Secondly I have too much useless and worthless coins right now, finding out there is a place I can gamble with that money gives them a purpose, I mostly lose all of them which is fine because I saw them as useless anyway but sometimes I win and just exchange it to bitcoin and withdraw.
Altcoins are much more flexible to gamble with than Bitcoin itself, as they're cheaper and faster to use. Not many online gambling sites accept a wide variety of cryptocurrencies. But those that do have a great advantage over Bitcoin-only casinos. Even though crypto has become extremely popular in the mainstream world, Fiat is still the dominant currency for casinos and online gambling sites alike. After all, Fiat is much more stable in price than crypto itself. It's hoped that an increase in the scalability of underlying blockchain networks would increase adoption of crypto within online gambling sites. Otherwise, the high transaction load would cause fees to rise making crypto impractical for micro betting and more.
A huge advantage of crypto towards Fiat is that it can be used without the need for ID verification. There are many online gambling sites out there (like the one under my sig) which don't require the gambler to verify his/her identity. This provides convenience above all else, as crypto can be used online as you would use physical cash in the real world. Anonymity proves to be wonders in the online gambling industry thanks to the inception of crypto and Blockchain technology. Better yet, decentralized gambling sites have no middleman or central operator in charge of the bankroll. This gives a greater level of fairness and trust from everyday gamblers than traditional casinos and gambling sites which only accept Fiat.
Nonetheless, it's hoped that the number of crypto gambling sites would increase over time. As long as decentralized solutions are being worked on (mostly in the form of smart contracts), most people will prefer to use crypto for gambling than Fiat itself. In the end, everything will depend on the specific person's preferences over one currency or another. You can't avoid Fiat casinos from operating within the mainstream world, the same way you can't do so with crypto. Neither ends will replace one another, which is good for diversity in the gambling industry. Just my thoughts