If you were picking a QB for this year you would be taking a big risk with Romo because he's missed games the last three seasons with injuries. That's the biggest concern we have with him right now is if he can stay healthy.
This post really isn't necessarily aimed at you, but is really to everyone who says that Romo is an injury waiting to happen.
Yes, he did miss games the last three years (2013, 2014, 2015) but in '13 and '14 he only missed one game each season. In those two years, his QBR was 97 and 113, with 65 TD's and 19 INT's. His 2014 season, in particular, was outstanding and put him squarely in the league MVP conversation. That MVP talk was less than a year and a half ago, and came in a season that he was recovering from disk surgery... a far, far more difficult and dangerous procedure than fixing a collar bone on a non-throwing shoulder.
Now, he did miss almost all of 2015 but that was with the previously mentioned clavicle break (along with re-breaking it on Thanksgiving). Not only is a collar bone injury something that NFL teams and doctors never worry about beyond normal healing (and was on his non-throwing shoulder)... but Romo also had a Mumford procedure, which will prevent further issues with that clavicle if he takes the same kind of hit that broke it. In essence, the team doesn't have to worry about that injury any more going forward.
It wouldn't be a stretch at all to say that Romo will be much better off heading into this season than he was heading into his MVP type season of 2014. That year he had to watch what he was doing because he was recovering from the much more serious back injury that had caused him to miss the final game of 2013.
So, while you are technically correct that he has missed games in each of the past three seasons, it was only last year that he missed any significant time... and that was due to a problem that isn't recurring and won't be an issue going forward. In fact, unless one contends that Tony's bones are more brittle than they were 10 years ago, no broken bones will be more of a problem than they have been for him at any age.
If you look at 2011 - 2014, Tony only missed 2 out of a possible 64 games. The only significant loss of play time came from the collar bone, which won't be a problem going forward.
Would I take Cousins right now for Romo. I'm not sure. I might, simply due to age. There is no question that Tony gives Dallas their best chance this season but thinking 5-6 years down the road, you'd be glad you made the trade. That is me assuming that Kirk will be an average to above average starting QB... which I think he has a good chance to be. I don't think he'll ever be as good as Tony, but most QB's aren't.
So, in a nutshell, I think Tony is better right now but I do think that Cousins can be a pretty good QB.