Just a heads up for Gamefly tips.
If you want a new release you have to put it in your queue before it comes out. So if a game comes out Tuesday, you need to have an empty slot by the previous thursday. And leave your queue completely empty. Otherwise they might send you something else. I've never missed a game on release day when I've followed these steps.
When it comes to games that are already out its a crapshot. They might send you anything in your queue but they always tend to favor higher availability. So if you really really want a certain game, you may have to leave your queue empty for awhile (and suffer not getting anything for awhile) so they don't send you something lower in your queue. If you actually don't care about which game you get among the released, then you can just fill up your queue as you wish.