Pretty much any o-line in the NFL is going to compare favorably to Denver's. From what I've read, Houston's o-line is solid, but not Dallas-good. Still, if Romo's thinking about his health (which he should be), Houston is the safer bet. Plus they're in a creampuff division so making the playoffs shouldn't be a problem, and a ring is presumably all Romo's playing for at this point.
Quoted from TheLaw:
Except he's, literally and sadly, 10 times the QB Manning was at the end. Meaning he can throw a ball 50 yards
Quoted from Deaconblooze:
I think Romo has more left in the tank than Manning did at that point, at least as far as throwing ability and movement goes.
Manning was a question mark coming off the neck surgery when Denver signed him, but he was superb his first two seasons here. Of course Romo has more going for him now than Manning did in his last season (you could say that for pretty much any QB in the NFL, including Denver's current QB 1 and 2). But Romo has a solid track record of serious injuries and chronic back problems, so I'd put them in different categories of risk -- Manning was an "if", Romo is a "when."
Doesn't mean it couldn't work, of course. Romo's got a great arm and as a Giants fan I've suffered through my share of his crazy shoot-out performances. I'm just skeptical that he can stay healthy long enough to make the kind of difference Manning did for Denver.