My husband and I have had both. For solo use I'm not sure it would matter that much, but I do prefer the DR for two people. It's easier to avoid bumping wet sides because of the mesh at the side. My husband prefers the Cloudburst, mainly because you can often leave the vestibule open when it rains. The DR is kind of a pain because you immediately have to put down two separate vestibules if it starts raining. Another issue with the DR is that if it gets really wet (such as heavy dew), once you start moving around and bump the tent slightly, water starts running down, hits the mesh area, and drips right onto our bags. There are a couple campgrounds that we camp at a lot where we had this problem, but it's not as much of an issue when backpackging where you can pick your site. We didn't have a problem with leaks once we got it seam-sealed, but it does take a while to get every seam inside and out.

The Cloudburst only needs three stakes to stay upright and the large loops make it easier to use objects other than stakes if you need to. The zipper in the newer Cloudburst design has a very sharp angle and we've had problems with it splitting after only a few months of use. Also, it's a lot of mesh flopping around when it's open, and hard to keep out of the dirt and easy to step on. Tarptent did replace our zipper sliders for free and said it was probably due to dirt getting in, but I think the severe angle of the zipper and the pressure on it in the corner is part of the problem.

For your criteria, ventilation might be a little better in the Rainbow. For ease of setup, the Cloudburst might be better, especially if only one person is doing it. The DR probably is better for wind since you don't have to orient it a certain way for best results. I think you're right that the Rainbow has a little tighter pitch because the arch pole keeps it from sagging as much as the Cloudburst does when wet. But the Cloudburst does have line tensioners for the front guylines in the latest model, so it should be easy to adjust the tightness without getting out of the tent. (We haven't actually used them because the lines are tied to a loop when you get the tent and we haven't bothered to move them.)

I don't think there's an obvious winner between them, both have pros and cons that you'll have to decide which you prefer.