Of course GBA is better than the NES. It is a technically more capable system with more coherent, better designed games.
Metroid Zero Mission is a better game than the NES original Metroid.
Every single Zelda game on the GBA is a more enjoyable experience than the Zelda titles on the NES.
Every Castlevania title on the GBA is better than the NES Castlevania games.
There really isn't a lot to argue here.