You're in a plane that's crashing near a desert island, and you only have time to grab one Dominion set before leaping out with your parachute. Which one do you bring? Assume you keep a spare box of Basic cards in your pocket at all times. Also assume that stopping to grab a box will not in any way endanger anyone else, or result in some indirect way in you all starving to death.
Oh man, who leaked that there was an upcoming expansion with edible cards?
In a desert island scenario I would just be concerned about survival. If I survive I will find ways to play games. So the question then is, which is worth more towards surviving: more cards, or metal tokens? I bet the tokens are not actually that useful, but then cards are unlikely to be useful either. The tokens at least give me something different that might be useful, so okay, whichever set has more metal tokens. Without checking, I don't know if that's Seaside or Prosperity (my experience is with the prototypes, and I just have a box of tokens for use with many games).
My favorite sets are Dark Ages and Adventures. It's hard to compare them fairly because Adventures is newer and there's that gulf in time between them.
If I am just playing one set by itself with Base Cards, then Adventures has fewer kingdom cards but more variety, due to Events, so that gives it the edge.