The first thing you must understand that it is not allowed to play online from US.
In Europe we have this opportunity. 

Secondly, if you must select a casino online, do this by knowing what slots you want to play.
Don't let the bonus offers and the welcome packages distract you.

Try out the slots from different online suppliers on pages with no advertising such as www.netent.com or read about 'em in slot libraries such as sirslot.com

Then all you have to do is to check whether the casino in question has the slots you like.
You can do this online, however I could not find any page offering this service without advertising, so I will not post any links here, as then this piece of advice might get blocked.

Greetings from Sweden!