I've been playing online casino slot machines for a while now, and I'm looking for advice on which ones are the best.
You can choose casino sites that are already proven for many years. Stake, Freebitco, Rollbit, Duelbit, Roobet, and Crypto.games are reputable casinos. I think these casino sites are some recommended places for you to play slot machines or other games. There are many people in this forum also played in these casino sites, including me as well. 
I do agree. that's quite easy to know which sites that are legit. Almost all of sites that you have mentioned above were legit. So many people are still actively playing there. He has so many reliable sites to play with. Im not feeling doubt about those sites. they are all having very good reputations in this forum and crypto users. OP must not feel so confuse to pick one from there.