Best harley seat i hear is The sundownder. Which will be my next purchase. But there's also corbin's and mustang seats. However i think your paying alot for the name.
The best buy out there for a comfortable AND affordable Sportster seat is the Harley Sundowner. Order one from Zannotti's for $198 and your done. Mustangs are also good and better built but also twice the money and I think they look too big on a Sportster.
I went with the Sundowner, I just couldnt justify the cost difference for the mustang or corbin. The Sundowner is the most comfortable seat that I have had on any bike that I have owned.