the golden sun series are the best rpgs on the gba- but they have a lot of puzzle solving in the game- some of which are pretty tricky- the battles are not too bad- they dont require strategy until you get to the later bosses
if you dont like the puzzle solving element in golden sun, then i highly suggest you look into lunar legend for the gba- the game's battles are not hard but the story in the game is pretty good- it is a good game
later this year they are coming out with a new mana game on the gba that i would highly suggest you look into- it looks pretty good- its called sword of mana
but since you also like action rpgs (like mana) then i would also suggest looking into the castlevania games on the gameboy advance- they have rpg elements where you gain experience points from beating enemies, and you pick up new equipment and items to help you progress through the game- it is very fun- the best game out of that series to me was castlevania: aria of sorrow- it was very fun, but it was a little short
if you have any other questions just ask- i hope this helps you a little