I played a lot of disparate time periods and blocks, going in and out whenever the winds changed too much or something interesting was on the way. I played the most in college, from Onslaught to Llorwyn/Shadowmoor. I really loved playing Onslaught block, I even remember my first two rares from my first two boosters then ... well, I remember Butcher Orgg and the other one I sold to buy 4 more boosters that day but I cannot remember what it was other than a black rare enchantment. Whatever.
From there, I remember doing Mirrodin and Darksteel drafts and tourneys (I made a Shunt Draft deck that when I drafted 3 of them and an Arc Slogger ... was just completely awful because of the sheer lack of things for me to shunt, but I do love that card still, as well as Arc Slogger who is amazing). Then came Kamigawa ....
Man, I loved Kamigawa (except for Soulshift, but that was relegated to Green/White/Black decks which were awful, so that's fine). Awesome rats, awesome goblins, awesome samurais ... what a cool set. I had all sorts of great decks and probably bought 3 boxes of it in college. I loved this set ... then Betrayers came out and just ruined the power-levels with the Jitte and the ninjas ... and then Champions came out and was awesome though it tried to do a mechanic about having 7+ cards in hand without ever giving a lot of ways to keep your hand that stocked beyond just slow play, so the Jitte still destroyed. But still, I loved Kamigawa to begin with.
Then Unhinged happened. And that was ridiculous.
Then it was Ravnica. And that's when I got into the most. I had block, tourney legal decks that I won stuff with. We drafted a bunch, I scoured eBay for cheap boxes, it was pretty great. The gimmicks were fresh and interesting, the guilds were all neat, the mechanics made everyone happy. Awesome stuff.
I heard a lot of bad things about Coldsnap, but I loved it! I wanted more and more, but my friends that played at the time all avoided it, which means I ended up avoiding it more than I wanted. I still super want just a box of Coldsnap, I like it so much.
Then came Time Spiral. The the color shifting that made me super upset because of how much I loved Magic theory. But that aside, it was a super cool set. I was currently getting into the history of Magic, the meta-themes, the old plots, and seeing all those show up again, all the references to the past, all the magic theory and stuff was so cool! And then planar chaos ... and the colorshifting. Ugh. Made me super unhappy. I didn't buy a single bit of Planar Chaos. But Future Sight was phenomenal! It did everything I loved from the first part, but in the future!!!!
Then Llorwyn/Shadowmoor. We played the crap out of those sets. 4 or 5 boxes, a bunch of tourneys and drafts, it was a huge amount. I really loved this set ... and I super hated it at the same time, which is why I stopped playing there. It became easy-mode. The power of cards were getting ridiculously over the top, and tribe decks were so easy to make that there wasn't competition and skill in deck-building any longer. It was just "I'm playing elves" and then spending more money than the guy playing Elementals. Or spending more money on Kithkin and that beating the guy who spent less on Merfolks. I was not immune to this, as I spent way too much money on a Treefolk deck. And it won. A lot. It was so strong it was basically indestructible. Oh wait, it was, because of Timber Protector.
Not only that, it introduced the most powerful and worst version of that exact complaint (about the game becoming about money instead of skill and cards being too powerful) with Planeswalkers. They are awful. Dreadful. Terrible. I hate them with every fiber of my being. And I know most people don't, and that's fine. And I know it is hypocritical to like a few (Koth and Karn, plus I like the old characters getting cards, not continuing to make more new planeswalkers ... where is my Squee planeswalker?!). But it just killed the game for me. The game was no longer something where I could spend time putting together a deck where everything cost only 1 CMC and it still had a fighting chance, because everyone else would just spend 300 or 400 more than me and have eight planeswalkers and a billion Day of Judgments and other ridiculous things. The skill was gone.
So I stopped playing.
Years passed, I moved away from all my college friends, got a divorce, moved back to Newnan, and Innistrahd came out. I love Ravenloft, I love gothic horror, and I was making friends who were interested in playing again. So I jumped in. And I kind of liked it. I played a lot of drafts, and it was fun for awhile. Transform is a pretty fun mechanic. Blue/Black zombies was a novel approach. Some of the cards are truly inspired. And I like the actual story of what is happening with the Planeswalkers, which is nice and all. But something was missing for me. So I stopped. And then I lost my job and needed money and sold everything.
Then I met my now very tight friends. And they reminded me of the joy of Magic. The fun of finding combos and doing ridiculous things like building a deck around having an incredibly low CMC or shuffling all the time or playing every card so that the game has to restart. The fun of magic is making a deck or a combination and just playing it. It isn't about spending money on the cards, or using the most Try-Hard I-Gotta-Win-Or-I-Don't-Have-Fun decks. It is about building a deck entirely around the concept of never being attacked, EVER ... or winning because you gave all your opponents a billion life ... or just playing a farmer working really hard to get his rot-farm off the ground.
Now, I say all this because I was supposed to be picking my favorite set/block. And I'm pretty sure I could answer this emotionally from my memories (Kamigawa) or from what I just liked to buy the most (Odyssey) I think the honest to god answer is that I don't care about any of the blocks. I like building casual fun decks and spending time laughing and getting upset and destroying each other and making none of Josh's decks work because we focus on him, and getting really upset because I get focused on when I pull out my best deck even though I know I need to be focused on because it is my best deck.
But that's just my opinion.