[Beebs]

It's close, but I've gotta go with Bolt:
-the sport is more participated in, by a huge margin
-The lack of any particuarly helpful new technology, sprinters aren't breaking records every race like swimmers are
-Smashed 2 records, one of which was thought almost impossible
-Won in a little more dominating fashion
-The 100 and 200m are probably as or more different than any of the swimming events, you always see swimmers win different events, you almost never see somebody win the 100 and 200, and I don't think there has ever been a simultaneous record holder in them.

Yes Phelps is awesome and has won more medals, but only a swimmer could possibly win that many due to the number of events in swimming