Well they're not that much fun on GBA. First of all Shining Soul is a RPG right, so it wouldn't be that much fun to play multiplayer, having no real features that differ it from the singeplayer game. Final Fantasy Tactics Advance however has multiplayer features that work very well when playing against other players, that's why it would be one of the best RPG/Strategy Multiplayer Game for GBA, along with Advance Wars,
Fighting games would also not be much fun on GBA. Firstly because Fighting games were originally made for Arcade Machines, and secondly because the controls on the GBA are just too inflexible to allow for proper tradionational Fighting Gameplay. The special moves are usually modified from the Arcade originals, or made to be assisted by the game. Fighting Games do not work on the GBA and Multiplayer is no exception. I really can't name any good GBA fighting games apart from Advance Guardian Heroes, that game was not a traditional fighter, but that was what made it so much fun to play. Highly reccomended. :)