For those curious, I kept the big Mustang.
I have had the Sundowner since I got the bike, and have about 5000 miles on it. The other seats, I rode for between 300-800 miles on, each. (not all in one ride)
1. The Ultimate COULD be a great seat (my wife vastly prefered it, out of the box, to all the others) but it needs more shaping and contouring in the rider section. The Memory foam is very good however. It shoves you furthest forward of them all. Also, it was only comfortable if I sat right in the "pocket" of the seat. If I moved around, scooted forward a bit etc, it was not as comfortable.
The Mustang Solo is good, but it sits so low because it has less padding. It was good for about 100 miles before I had to get off however. The low lip on the rear of the drivers section did bother me somewhat, even with the backrest on.
I personally really like the Sundowner, but the Wife cant ride on it for more than 30 miles. The passenger section is just too small and too hard. I SUSPECT that in time, with enough miles, the Foam in the Sundowner would break down and collapse more than any of the other seats. Its just not made as robustly as the others. So while its comfortable now, I suspect it may not be in 10k miles or so.
The big mustang is simply the cushiest of the bunch. Its padded the most/best, and it supports you the best. It does sit you up a good inch higher than the others, but its about the same as the stock touring seats (ElectraGlide) in position, in my opinion.
Having said that, I had the Mustang modified:
1. had the drivers section lowered .75" and moved back .5 (as far as we could go and still use the existing cover)
2. Had a .75" thick cross-mesh jell pad put into the passenger pillion (wifes butt is just too damn tender!)
3. Had the nose of the passenger section narrowed a bit and rounded off at the top edge.
I may still Add a half inch of memory foam overall.
My wife could only go 60 miles on the sundowner, and was in PAIN at the end. (not just a tired butt.... she was seriously hurting)
60-80 miles on either of the Mustangs, as they came out of the box.
She did 170 miles on the Ultimate (memory foam) with 1 break, but was a bit uncomfortable at the end.
She did 180 miles on the modified Mustang, (cross gel) with 1 break, and felt fine when we got home.
Having said that, she is 5' 4", about 140 pounds, and she just needs a really cushy seat to be happy. Moreso than anyone else I have ever known.