I've warned people for years that extreme and brango have their games set to pay out terribly. It can be tough to be 100% sure from playing slots between terrible luck and bad games, so the real giveaway is their video poker. They don't offer the standard payouts, like normally jacks or better is 99.5% but at extreme/brango it will be like 95% payout.
Slotland is a weird one. Their games do NOT pay out like normal slots, they are more like scratch cards. So on many of the games you will never actually hit top 5 of a kind. Not sure if this applies to their new slots, but if you try just playing 2 lines on their older slots, every dozen or two spins you'll see the screen littered everywhere with the top symbol. But it will NEVER actually hit your lines on those games - your odds of hitting it are probably the same as hitting a 200k progressive jackpot, because it's often connected to it (but you don't qualify without like a $10+ spin.) The reels are just for show. They got called out for this (it was reported by the wizard of odds guy) when the chance of hitting a royal flush on their video poker games didn't match the actual chance if they were real playing cards.
Despite that, the games would still be playable if they have a reasonable RTP and distribution of results. They offer a once a month bonus with only a 10x wagering requirement, so sometimes you kind of wonder if they can offer that without their slots being complete money guzzlers. I tried playing that, a 150% bonus with only a 10x wagering requirement, sounds pretty good? Well, I went for over 200 spins only hitting a SINGLE scatter. I don't mean a single feature, I mean one total scatter in 200+ spins. It was so bad/bizarre I almost made a post about it. I didn't even start counting until I noticed it was weird how no scatters were coming. On a normal slot something like that is an impossibility. Didn't even bother with my last 37 cents or whatever and just left.
I think they used to be okay, but I really don't know if you're getting a reasonable game there now.
With that said, my luck is almost incomprehensibly bad everywhere so it's tough to say for sure. Bovada group is definitely the best choice if their games pay out the way they are supposed to. They sure haven't for me, but someone has to be unluckier than 999/1000 other people I guess? Again, if their games pay out how they're supposed to, they really do seem like the best choice available. Aside from that, there's still 3dice if you like their slots, though I think their promotions are a little boring.