It depends on what you want:
Tactics Ogre: More traditional story, somewhat bland characters mostly, almost as easy as FF Tactics Advance. Neither has much challenge compared to their big brothers, but both are pretty fun. It is far less complex than Tactics, as there are very few skills to get in the game. The story is pretty good and it has two endings and some alternate characters in each branch.
Fire Emblem: Not as long as Tactics if you are good, but it is much harder and has much more interactivity on each map. I found it much more satisfying. It has a great story, great characters, and a fairl complex world. The art is quite good, especially in the cut-scenes.
Advance Wars series: No RPG element, but the best strategy gameplay on the GBA, or any console perhaps. I prefer Fire Emblem for the RPG elements and the story, but it is nice not having to worry about losing units as all are generic military units. You would be best served to ignore the story completely, but 2's is not as bad as 1's story (I like you, but I'll challenge you to fight, ignoring the hundreds of soldiers who die in each battle under the command of a child).
Also, did you complete the post game missions and the Judge missions? I did like the fact that you can lose units when you battle the Corrupt judges.