Have I replied to this yet? Dunno... Anyway!
My favorite sets... I think I'll rate them like Giz did above, but I'll only do the ones I really interacted with at all:
Revised: Eh, my first set, not my fav, but I did get a Lightning Bolt and Lanowar Elves in my first Starter deck.
Legends: To this day, Legends to me seems to be the pinacle of the "old days." I guess because the story of a Golden Age within the cards and the introduction of Legends creatures themselves were just so cool. I've always had a affinity towards Legendary creatures because of this set. Unfortunately, when I got into Magic, packs were $20 a pop, way outta my league.
The Dark: Is it just me, or was The Dark almost a heralding for the actual future of Magic at the time? The Dark, a descent into death and Fallen Empires. Almost prophetical in a way to me. When I got into Magic, these were $8 a pop, way out of my league again, so I didn't ever see much of these. But God, did I want a Maze of Ith!
Fallen Empires: The cheap set, the set I could afford. The set I LOVED! My favorite combo: Basal Thrull and Soul Exchange. I used to sacrifice the Basal Thrull for BB and then use it for the Soul Exchange. Yes, yes, I know that's not legal now, but it was killer back then! (Soul Exchange would be a good reprint, by the way. It's a balanced version of Recurring Nightmare.) To this day, my little brother's favorite combo is turn 1, Goblin Chirugean. Turn 2, Goblin Grenade, or turn 1, Dark Ritual, Hymn to Tourach, Initiates of the Ebon Hand.
Ice Age: Never had many of the cards, didn't like the set a whole lot, besides a few exceptions.
Homelands: Call me strange, but I really liked this set. Minotaur decks just rocked because of this deck (in casual). I loved Autumn Willow and Ihsan's Shade. There were a lot of really balanced, yet, fun cards in the set. And I liked the story as well.
Alliances: Ah, here's a set that just truly shined! Great story, great cards (yeah, every set has some bombs). Everything was balanced.
Mirage: I went to the prerelease for this and didn't stay all day. I found it to be slow and boring to wait and games were fun. Everyone was unfamiliar with the cards and the set was fun.
Visions: Ever set needs to have this many good common cards. One of my personal favorites simply because of one card: Viashino Sandstalker.
Weatherlight: Good set. I didn't get to play with it yet, but it has one of my favorite artifact cards: Well of Knowledge. Does anyone else but me see the inherent strength of this card in your deck? If you can draw cards AND play them, you have all the advantage! If your opponent uses it, then they will be slowing themselves down. I'm telling you, this is one of the best card drawing engines of all time. Metal Worker and Well of Knowledge just rock together. Through in Mind Stones for mana acceleration and it's cycling ability and you have the basis for an extremely strong deck.
Tempest: Good, has Cursed Scroll and Slivers. That's all I have to say about it.
Stronghold: YES! THE MOX IS BACK!
Exodus: Paolo Parente's artwork is all over this set. COOL! It also has Mirri. What a great set.
Urza's Saga: Broken cards, strengthened green though. Hmmm... I kinda liked this set, but I couldn't get enough of the power cards for any kind of competativeness.
Urza's Legacy: I LOVE THIS SET! I'm partial because I won a full foil set, but this set has Rancor, the greatest green common ever made, it had Grim Monolith, it had Weatherseed Treefolk, and a bunch of other cool stuff that wasn't broken (yes, there are exceptions), just good. All sets need to be at least this caliber.
Urza's Destiny: I feel I never got any of the good cards from this set when I bought a box. I had to buy my Masticores and I never got more than one Yawgmoth's Bargain. It's a power set, like Urza's Destiny. It's a set for those who have lots of money.
Mercadian Masques: Brought creature battles back. Very good. Kris Mage is just cool art. I love this set. Rebels are cool!
Nemesis: GREAT SET! Balanced, except for Lin Sivvi. I NEED MORE OF HER!
That's my opinions!