Rentals can't hurt your pocket too much
Probably the best in the AC series was Silent Line, if not for the awful control schemes that had been around for such a long time.
Mech Assault 2 was full of gimmicky stuff last I recall. Wasn't any customization either. None of the finer points of mech games.
Not going to knock World of Tanks before I check it out, since I've heard a lot of good stuff about it from our program director at the school I go to. He had a hand in developing the game.