It's pretty much all theory who's the strongest human. There's nothing in the manga besides Yamcha saying Krillin is the strongest human and maybe Tien getting Buu's attention with a Tri Beam.
Unless you go by Filler where Yamcha easily beat the guy who barley lost to Pikkon who KO'd Perfect Cell with one kick making him the strongest.
--
http://img401.imageshack.us/img401/33/shadowkenj.gif
LOL!!!! I hope that's a joke....names don't get more n00bish than that