best gba flashcart for gbaSP/gba?

I wasn't sure if this was the right place to put this but I figured since the NDS has a GBA slot it might be ok here.


I was wanting to maybe purchase a GBASP again but I want to get a flashcart for the GBA port. What is the best one I can get? I should note (if this matters) I want to use it on a GBA not a DS(I want to get two so I can trade pokemon back and forth/play MP games with my other friends SP)