>>583
I'd host anything from the alpha vesions to 1.6.2
Where I draw the line is that they changed flower placement so that it's not in the center of the block and made roses into poppies. They also gimped the oceans and caves in that version which makes the world less fun to explore. If we did 1.6.2 it would have the advantage that there are horses for one thing. There would also be more options for technical builds with hoppers, droppers, comparators, and daylight sensors.
If we did 1.2.1 we would get a unique world generation that is my personal favorite where the forests look different than any other version because of a bug. I also know a lot of fun glitches for that version like breaking bedrock, duplicating sand and using it to make belt machines which opens up redstone in interesting ways, and cosetically altering blocks to get otherwise unatainable varients.
If we did Beta 1.7 we could potentially move the spawn point to the far lands, although the gimick of those wears off after a while and they are a very unwelcoming place.