Rupert gets my vote, all the way....
I never had a big problem with Rob. He manipulated, certainly, but he did it strategically. Other people in his position in the past have been arrogant to the point of thinking nothing could go wrong, which is why so many of them eventually get booted (think Johnny Fairplay).
Rob was certainly arrogant, but never took anything for granted (except Amber's allegance).
Personally, I predicted the marrage proposal before the episode even started. The thought did cross my mind that it was to make sure, but I think it was genuine.
As far as what happened to Rupert, that was another "plant the seed" move by Rob. Apparently, it was announced that the tie breaker was the purple stone. Anyone without immunity had to pull a stone from a bag and the purple stone gets the axe (same thing that happened to Pascal way back when). Basically, at the very start of the episode, Rob and Amber told Jenna that they would be voting for Rupert and if she wanted to protect herself from the tie, she should do the same thing.
I'm a bit disappointed with Jenna for actually doing it, but she didn't want to take the 1/3 chance of getting booted herself.
Realistically, I think she should have realized that making it into the final 2 at that point meant having to beat out them both, whereas if they were lucky enough to hit Rob with the purple stone (Amber won immunity - Rupert was a reasonably close second), then either one beating out Amber would get her into the final two.
But, again, she was so concerned about making final 3 that she didn't consider final 2, so she voted with Rob and Amber to eliminate Rupert.