i choose the super game boy monochrome.
definitely a close second for me on the background alone, i like how it gives a colour book esq feel, kinda fits pre WL4 era wario.Really like the GBC choice personally.
There's a thread here showing the only difference and that would be a fish being slightly bigger, its literally the exact same as all gameboy games though.I didn't know there were several! It'd be cool if you post the pics of each, or at least a few of them so we can compare.