So I've gone into the 12w21a snapshot a bit and generated some sample worlds for demonstration, as well as to get user preferences.
Methodology used:
1) Use server jar and properties file to create a Creative mode world with any seed I choose.
2) Exit server, generate more land (configured to 1536 x 1536 to speed up testing - I predict the actual map sizes to be anywhere from 5120 x 5120 to 8192 x 8192) with MinecraftLandGenerator
3) Generate in-game map of the 1024 x 1024 area surrounding spawn point, since this will probably be the most active portion of the map
4) Post screenshot when done (I could use Biome Painter or other tools but those are mostly for 1.2.5)
SEED 1 - kanako_yasaka
Spawn Point: X -162, Z -9
Fair amount of both land and water it seems. Pretty clean-looking too.
SEED 2 - alice_margatroid
Spawn Point: X 220, Z 246
First time I ran this, it hilariously didn't have any blocks! A second run fixed things at least.
Great amounts of land and biome variety, but it seems a bit cramped.
SEED 3 - byakuren_hijiri
Spawn Point: X -48, Z 250
Sparda's comment on the massive oceans: 'murasa at work'. :V It might work better if it was a Large Biomes map, but for standard...unless we were doing territory wars I wouldn't see this working.
SEED 4 - futatsuiwa_no_mamizou
Spawn Point: X -15, Z 248
Full of jungles, desert, and water (swamp in south, ocean in north) around spawn, not a good mix for newcomers if you ask me.
SEED 5 - yuukarin_kazami
Spawn Point: X 188, Z 257
Plenty of land and lots of biome variety. However there's already a mega-ocean on the northwest.
More seeds will come in later, as well as with upcoming snapshots.