I have no experience with the Haven, but I am a Stratospire 2 owner. I've never looked over the Haven particulars, but did so I could offer a response. First, the comment above about the offset doors is a non issue. My wife and I sleep with our heads on the same end and it is no problem entering or exiting from either side. Second, based on the mfrs measurements, the Stratospire 2 has 5 inches more interior height and 4 inches more interior width. Both of these are important to me as I am on the tall side so I appreciate the extra headroom. Also, my wife and I both own and use the large NeoAir pads, which are 25" wide each. These apparently wouldn't fit side by side in the Haven with its 48" width.
As for setup difficulties, I can't imagine either one is any different than the other once you've done it a time or two. Tautness was not an issue as its easy to adjust the stratospire once you have it erected. Of course, raising the poles a bit from inside the tarp is very easy to do, too. That will tighten it nicely.
Vestibules on the SS2 are huge. Can't speak for the Haven, but it appears the Haven's vesties have a smaller footprint based on a simple visual comparison of the drawings on each mfrs website.
Take my comments understanding that I have not done an in-person side-by-side crawl around inspection.