There are not many powers that would be as good as better then being able to see not only all the cards people are holding but all the cards in the shoe. You would be able to tell what everyone was going to be dealt before the hand ever started. With an advantage like this you could take the casino for all their money.
Cloaking:
Cloaking is the ability to become invisible or make your self look like something else. Alone this power is not the best for cheating in a casino, but in a team it can be amazing. If you can make yourself look like a roulette ball then replace yourself with the real ball. Then you can land on whatever number your partner bets on. Or on craps you can make yourself look like the dice and land on a winner for you each time.
Plastic Man:
Cool power but I don't think it would be so great for cheating. If you tried to sneak your arm under the table and around the other side someone is bound to notice an arm popping up and moving chips around. This could maybe be good if you can get your arm inside of a slot machine and make it pay out.
The Thing:
The things super power was that he was made of stone and had almost unlimited strength. This would be good if he wanted to become a professional wrestler or an UFC fighter. He would be undefeatable. How to you punch something made of stone. What submission hold works on rocks, but how strong you are is no advantage to cheating in a casino.
The Human Torch:
Fire + Casino = Bad!
Aqua Man:
I did hear about an underwater poker tournament once, but in a regular casino this would be useless, maybe if there was fish tanks all around the room then I guess it would work.
Using Your Brain:
Call it whatever you want, but the ability to move things with your mind would be a great help in a casino but not in every game. You would not want to sit at the poker table or the keno room with this power. It could be good for the slots as long as they are not video slots. This power would be best for the roulette or craps table.
Mind Reading:
This would allow you to know what the other people had in their hands but unlike X Ray Vision you would not have a way to know what the next cards were going to be.
Ability to Manipulate the Weather:
About the only thing you could really do with this is to make the casino foggy and change the results of the game.
Storm:
The ability to control the weather would have no effect on any casino game. Maybe you could make lightening strike the slot machines and hopefully they will start to pour out their money.
Ice Breath:
The ability to freeze everyone in the casino again is another talent more practical for a thief then just a casino cheat. This would be a great skill if you were throwing a party. You could keep the keg super cold, but do not see it working in the casino.
Power of Suggestion:
I don't care what super power you have this is the best one you could have for cheating in an online casino. With this power you don't have to have a good hand or have to move the dice or roulette ball. You just have to make everyone think you won and take your winnings. You could be playing poker and have a 2,3,6,9 and a jack in your hand and tell everyone it is a royal flush and they would think it was the truth.
What is the point of having a super power if you can not use it to get stupid rich in a casino?