Do you think you could have asked a harder question, Tom?
Okay, I started with Revised and Fallen Empires, was wowed by The Dark and Legends, and bought my first box with Homelands... I can't choose...
I like the following sets best:
The Dark--> Love the opposition mix-ups (Electric Eel, Elves of Deep Shadow), but overall, The Dark was kind of weak.
Fallen Empires--> You know, this set really did not suck as much as everyone thinks it did. Here, I'll prove it:
Aeolipile (colorless burn, not bad)
Derelor (actually, he's pretty decent)
Goblin Grenade (one mana, one Goblin, FIVE DAMAGE?! You haven't played Sligh until you've been killed by four goblins which are immediately followed by four Goblin Grenades. Trust me, it can happen.)
High Tide (gee, didn't this spawn a rash of bannings...?)
Hymn to Tourach (best discard of all time maybe?)
Order of Leitbur (who didn't use this in white weenie decks?)
Order of the Ebon Hand (repeat as above with black instead)
Rainbow Vale (This thing is just plain fun!)
Thrull Retainer (This is not a bad card at all. A weak Unholy Strength until you need a Death Ward.)
Homelands--> Decent set for the thematic player. Balanced. No broken cards and maligned for it. And then people complain because Tolarian Academy and Time Spiral get made...
Alliances--> Balanced with very strong cards. I have yet to see a set besides Visions equal the strength, but where Alliances was strong with it's rares, Visions had all the best commons.
Visions-Good set. Let me repeat GOOD SET! A great set. Balanced, strong, one of the best of all time definitely.
Weatherlight-->Great rares (Well of Knowledge, Lava Hounds, Bosium Strip)
Tempest-->This sped up the game. Great creatures, great artifacts (Okay, okay, I admit, I really like Cursed Scroll... I know, I'm bad.) But it did speed up things too fast.
Stronghold-->Two words: Mox Diamond. Has anyone ever truly broken this? I don't think truly. Yes it borders on broken, but no. However, this set could have been stronger.
Exodus--> Yes, I know it's a broken set, but it brought out two of the best green creatures of all time in my opinion: Mirri, Cat Warrior and Skyshroud Elite. Could Mirri be anymore broken?
Urza's Legacy-->I'm partial to this set because this is where green got the strongest boost and I happened to win a complete foil set from Wizards. Rancor anyone? Fatties out the hind-end, good artifacts, very balanced. And the man-lands were just great, especially Treetop Village.
Nemesis-->Great set, nice green creatures and very balanced. Also added Lin Sivvi, who is just cool as all hell (yes, again, I KNOW she's broken.) And Complex Automaton is really not a bad card, I promise.
So my favorite sets are:
Legends (Legends are just cool, period.)
Visions
Exodus
Urza's Legacy
Any questions?