Bob was awful. The only reason he won was because that crappy alliance he was apart of (Marcus, Corinne, Randy, and Charlie) didn't want to accept that fact that the other alliance outplayed them.
They were spoiled, hypocritical brats, but even after the show was over they trashed Bob and said they only voted for him just out of bitterness towards Susie and Sugar and that Bob didn't so squat the entire came except lay around camp. I remember Corinne saying that whenever strategy talk would come up, Bob would just leave and never talk to anyone. He was the worst.
Vecepia, Tina, and Jenna are so underrated it's ridiculous. Tina was the leader of that entire alliance with Colby and Keith for the entire season and ran that entire game. She had Colby wrapped around her finger and got him to make the biggest blunder ever of taking her to the F2 instead of Keith, which would have given him a sure win.
Vecepia is another underrated one. She was very sly and worked the alliance hopping strategy to perfection. First creating the alliance with Sean R. and Rob M. that controlled Maraamu. After the switch, she distanced herself from Sean R. and Rob and cozied up to the Rotu 4, then she flipped back and helped create the counter alliance that took out the Rotu, than she made that last ditch effort the final IC throwing Kathy under the bus and getting Neleh to take her to the F2. Not to mention her great foresight in bringing the notebook/pen that lead to her F4 immunity victory.
Jenna, truthfully during the season I didn't like her, but looking back her win was a big turning point for Survivor. It essentially changed Survivor from just being survival of the fittest to being a hardcore social game. She built up the relationships with every single player that made the jury that season then went on to the end game game winning two straight immunity challenges tying Kelly Wigglesworth for women with the most immunity challenge wins (four). She swept the votes against Matt because he was a social dude. I really respect her game looking back at it.
If I had to pick the worst winners I'd definitely say they were Bob, Chris (Vanuatu), Amber, and Danni.
As far as Cirie, seriously. She owned both seasons she was on, there's just no way around saying she didn't.