If it's the worst based on the performance in the Finals series, it's Kobe.
Sure he puts up 27ppg, but on 40% shooting?
On the other hand, there is MVPau, where he posted 19/12/4/3 for the entire series, stood his ground on defense, had a 122 Ortg and a net +21 pts per 100 possessions.
Billups was unquestionably the leader of that Pistons team. He had far and away the best WS for the entire series, the entire Pistons offense was anchored around him. His ORtg in the finals was off the charts (133, while the next best Piston was Rasheed at 114), he played decent defense, and he shooting lights out against the porous Laker perimeter "defense".
Cedric Maxwell was leading the team in scoring, and put up 10 rebounds as a guard vs. the Rockets. The Rockets Malone caused all kinds of problems for Bird, and Parish, and Maxwell, capitalized.
Jo Jo White probably has the next strongest case. It was very similar to what Kobe did vs. the Celtics, where he shot a lot to get the highest scoring average, but his shooting percentage and other aspects of the game were easily eclipsed by a teammate big man (Dave Cowens in this case, who should have been the real MVP). His 33 points in the triple OT win probably won him the award, but from the overall perspective, Dave Cowens was the guy for the series.
Finally, Rick Barry was a great player, people forget that. Monster prick in his days, and probably a worst person than Jordan or Kobe, but he was easily the best player on that Warriors team.
Again, just based on the performance in the finals series, I rank the Finals MVP as follows:
Barry, Billups, Maxwell, JoJo, Kobe (the last two are real close)
Based on career:
Kobe, Barry, Billups, Jojo, Maxwell.