Krillin is the strongest human obviously toryiyama the creator of db, dbz, dbgt, etc. stated this multiple times in the series.
And he posses the strongest attack in the series "Destructo Disk" able to kill anthing the fight with the saiyen a would've been over in less than one minute if krillin had thought of it sooner. But then again where would be the suspense of the fight. Goku it the main character anyways so they give him most of the credit.(a little too much in my opinion)