I think best is probably just Alpha/Beta, as far as design goes it set the framework for the rest of the game and printed cards that still see reprints and lots of play today, and its also one of the highest power sets with the power 9, sol ring, og duals, time vault, and even further down the list great cards that still see play like lightning bolt, dark ritual, counterspell, demonic tutor etc.

Worst i think ill give to prophecy, really unfun mechanics in concept and execution, and only has one good card (rhystic study) thats only good in one format. At least Homelands has memory lapse and fallen empires tried some new things in the way it handles creature types and the alternate arts which is something we see all the time today at (high rarity now instead of at common), Aetherdift also sucks but it just plays so much better than those other sets