Most of the truly one-hit wonders, were that because the music really wasn't that good. I don't know about best, or what constitutes a hit, but here goes:
T Rex: Bang a Gong
Blue Image: Ride Captain Ride
Argent: Hold Your Head Up
Stories: Brother Louie
Malo: Suavecito
Norman Greenbaum: Spirt in the Sky
Vicki Lawrence: The Night the Lights Went Out in Georgia
Rick Derringer: Rock and Roll Hoochie Koo
Thin Lizzy: The Boys are Back in Town
The Buggles: Video Killed the Radio Star
Reunion: Life is a Rock
Wild Cherry: Play that Funky Music
T Rex: Bang a Gong
Blue Image: Ride Captain Ride
Argent: Hold Your Head Up
Stories: Brother Louie
Malo: Suavecito
Norman Greenbaum: Spirt in the Sky
Vicki Lawrence: The Night the Lights Went Out in Georgia
Rick Derringer: Rock and Roll Hoochie Koo
Thin Lizzy: The Boys are Back in Town
The Buggles: Video Killed the Radio Star
Reunion: Life is a Rock
Wild Cherry: Play that Funky Music