Puttin our personal biases aside is like a judge telling the jury in a criminal case to "ignore that last statement". It's sort of impossible to do so completely in either instance.

SMB was the first game that I personally owned. Lots of memories. It's an amazing game.

I didn't own AK:MW until I was much older, so I don't have any warm fuzzier for it. I really liked playing it, but by the time I picked it up the PS1 and N64 were sucking up most of my gaming time.

I can't say with 100% certainty which is the "better" game. I really feel that both were great titles worthy of their place in the canon of excellent, iconic and influential games. It's too bad that the Master System didn't receive much love here in the US. It was a powerful machine for its time.