From what I see, there are 3 main feeder bots: 16, 125, and 4334.

16 was very maneuverable, and had a great ball pickup.

125 had a great ball pickup, great strategy, and an excellent shooter.

4334 could pick up balls like no one's business, and fed their alliance to IRI victory.

Here's my opinion:

16, while fast and maneuverable, couldn't send balls over to the other side really quickly. They had to go to the bump/bridge to release the balls, since their catapult, while accurate, was too slow for feeding.

4334 was plagued with the same problems as 16.

125, however, was just amazing. They were quick, agile, and with their amazing drivers and shooter, were able to pick up any ball, and quickly send it over to their alliance side. The reason I choose 125 as the best feeder over 16 and 4334 is because of their consistent and well performed execution of the feeding/starvation strategy. In most every single match 125 was in, you could clearly see the constant stream of balls flying across the field from their shooter to the other side. They were so good at their role, that every match they forced their opponents to venture to the other side of the field to get balls. They even would pick up balls that their opponent's feeders would put on their side and shoot them right back. Because of their excellent execution of feeding, I vote 125 as the best feederbot (so far) of 2012. 256 did pretty good, too...