If I sat down and really thought of every variable needed to make a 100% accurate comparison, this list may be different, but in the meantime...
Quarterbacks with at least 60 starts, fewer than 80 TDs, at least 54 interceptions and a 59% or lower completion percentage, sorted by completion percentage, from lowest to highest:
Lamar McHan (42.3%)
Mike Phipps
Mike Livingston
Rick Mirer
Tony Banks
Dave Brown
Kordell Stewart
Joey Harrington
Rodney Peete
Jay Fiedler (58.7%)
This math includes Cassel's season in New England.