Tactics Ogre for PSP is my favorite game for that system. It really is an awesome tactical RPG. Like most tactics games, the battles do get a little repetitive once your characters are overpowered, but Tactics Ogre LUCT is less guilty of this than most games. The World system that lets you travel to any point in the game after you beat it is also pretty sweet and I hope that gets implemented in more games in the future.

I've only played the Ogre Battle series briefly on the first Ogre Battle game for SNES. I never got into it and found it kind of boring.