Assassin,
All three books will pay you. The difference between 7palms and roayl and grande is that 7palms is truly menat fr the square player. If they percieve you to be a sharp player, they will let you play, but you'll have to call in all of your bets. One of the reasons why a lot of people like 7palms is because of its "opinionated" lines. But sometimes those lines aren't opinionated, rather they are simply stale, and the linesman haven't gotten around to updating them. So what has happened to a number of people who use multiple outs, and only bet on the best line, is that they get labled as a sharp player and 7plams will no longer allow them to place bets online. If you plan on just using a single book, this shouldn't be too much of a concern. And if you're an average player, it's one of your bets bets because you get a true dime line with a 10% bonus.
My advice is if you are looking to bet more than a nickel a game you should go with grande or royal. If you are looking to bet a nickel or less, I'd go with 7palms. the worst that could happen at 7palms is that they cut your online limits. But they will still pay you. So if and when your limits get cut, you can move on. But until that happens you should have a pretty enjoyable experience.