Here in California, I have been seeing mostly 4/6 WDs, lots of interesting omni setups, and a few mecanum drives (my team is the only one I've seen so far with non-AM mecanums).
There was one very interesting omnidrive at SVR (I think it was team 362) that used two wheels on each side of the bot, with each pair parallel to its corresponding side. Pretty wicked looking
I also saw one with AM omnis arranged at 45 degree angles, much like mecanums.
I really like 254's 6WD drive. It's not only faster than my team's mecanum bot (which can go about 13-14 fps), but it can
turn on point better than us
Even though it has a significant lack of pushing power, the agility is beautiful.