I would start Hasselbeck, they play STL so he should have a big game. The Giants D picked up where they left off last year and look awesome, so I would not play anyone against them.
Go with Romo, San Francisco shut down one of the better offenses in Arizona to only 16 points, now they will face a weaker offense which should put up less points, great D or not, I'd go with Romo simply because he has better talent than New york, plus they are at home in that new stadium. But this is not our team, this is yours, we can only offer our advice, its your decision.
Start Romo, I will tell you why. Romo is 4-0 in the regular season since hes started, against the giants Defense. Sanf Fran has a great defense and yeah hassellbeck would be okay, but Iam telling you Romo has a history of owning the Giants D in the early regular season...Romo for sure.