Warb Null wins this in my opinion.
Tavion (possessed) fell to Jaden Korr, who was an above average Jedi Knight in the brand new Jedi Order. Jaden had fought through her entire force of Reborn and Cultists alongside his/her fellow Jedi Knights and still managed to defeat her. She doesn't seem to have much riding for her.
Warb Null was defeated by Ulic, who was absolutely Jaden's superior.