Spiderman,
You are correct in that I did intend this topic as a discussion about the Blocks, starting with the 1st declared block, Ice Age, through the current block, Mercadian Masques. I don't have a problem with anyone who wishes to mention an earlier set though. I was planning on trying to do a separate vote on favorite set, but first I've got to figure out how to cut the choices down into something that will fit into the Voting Booth program! There's a 20 choice limit...
Maybe we'll do a top 10, based on topic discussion in a thread like this.
My personal choice of best Block is Mirage/Visions/Weatherlight, because of the reasons Y listed. In my opinion, none of the other sets matched it in terms of fun, balanced play. The mechanics introduced were interesting but not overpowered, at least not once 6th rules straightened out the timing issues on triggered effects (sort of). And all the colors were viable in draft, from what I remember, though the Blue flyer/phasers were a little weak. The series wasn't much for theme/storyline either, but I've never really cared all that much about that.
A thoroughly enjoyable block of cards to play with.