My Favorite Set (or Sets) is Mirrodin. Because that was when I realy startet collecting.
Then there were a lot of sets i didn't care about... and... then
Zendikar happened O_O
So interesting. All those OP ally-cards and what not.
Rise of Eldrazi happened.
I am a casual Kitchen-table player... but i bought 2 displays of this Set.
And then they returned to Mirrodin and i was like: "I dunno"
AND THEN!! New Phyrexia.
bought 3 or 4 Displays of that.
The return to Ravnica catched my attention again.
I can't wait for the return to Zendikar and New Phyrexia. I probably die of old age before the later one but i can still dream.
I haven't played the actual card game in years, but I do enjoy messing around on "Gatherer" every once in a while and just seeing all the new cards.
Anyway, my favorite set is definitely any of the ones that focus heavily on Phyrexia. The creepy industrial/organic look to the cards is ultra cool and very distinctive. Even the creatures that don't have mechanical parts just "look" Phyrexian. I also thought it was interesting that there aren't really good colors vs. evil colors in Phyrexia, they're basically all evil, just in a different way.
My favorite expansion? Shadowmoor/Eventide. Much fun drafting there...
However, here lies my problem with the new unified podcasts. I simply don't give two shits about Magic any more. They killed off any and all interest back when M2010 noobified the rules. It's not just that the rules were changed, though the changed rules are immensely stupid (ie. the conga-line of death that Blocking has become), but it's how they changed the rules that pissed me the most off. Asking a bunch of people that didn't know how to play how they thought the game should be played, then changing the rules. It was a slap to the face of the judges that actually bothered to learn how to play. I resigned my L2 then and there.
My favourite set is the Kamigawa block. And I'm really sad that they will never revisit it. It was a kickass set.
I started during Innistrad and yeah it's easily my favourite. I love tribal, especially human\solider ones and there are some really sweet ones in Innistrad, also zombies yay!