Moymuffs has Russell Day Long (RDL) seats. Many of my long distance riding friends have RDL saddles as well and enthusiastically recommend them. RDL acquired the patent for internal spring support from Bill Mayer, Sr.
I have a Bill "Rocky" Mayer seat and like it very much. I have many years and tens of thousands of miles on it. Rocky is the son of Bill Sr. I highly recommend them. This is my first and only custom saddle. It has made a world of difference in my enjoyment of Iron Butt rides.
The seat still looks almost new. Rocky gave me a bottle of Bee Natural "Leather Amore" and told me to put it on once a month (rub it in like hand lotion). It has done a great job protecting the seat from all kinds of weather.
Stay away from Rick Mayer (another son of Bill Sr.). Rick Mayer has had some personal issues in the last few years. About a year ago, several people reported that he closed shop and disappeared with their seat money. If you were lucky enough to get your seat back, sometimes it took six months or more. He also has a reputation for not communicating with customers. Even if he seems to be in business now, I would not risk my money with Rick Mayer.
RDL, Bill "Rocky" Mayer, and Rick Mayer saddles are all "descended" from Bill Mayer, Sr.'s business, saddle designs, etc.
Corbin has a mixed reputation. Some people love them. Others had bad experiences with delays or poor support (e.g., hostile reactions) when issues arose.
Sargent - I know very little about them, good or bad. Perhaps others can chime in.
Things I learned about custom motorcycle seats:
* They will raise your feet at stops. If you are on toe tips now, a custom saddle will make it worse or impossible. Don't believe what they tell you about lowering the seat. Custom saddles are thicker (for comfort) and also wider than stock, so you may have to slide forward to plant your foot if you are marginal at stops now.
* Custom saddles need time to break in. It can take 1,000 to 2,000 miles before you achieve that maximum comfort level.
* The first fitting is not always perfect. I did a ride-in fitting, but it was my first time buying a custom saddle. They were very patient, and kept asking me where were the pressure points, etc. The original saddle as fitted was too soft in spots and too hard in another. After the break-in period, I did another ride in, and they fixed the issues perfectly. That saddle has been a joy to ride. The next time I get a custom saddle, I will know what to expect and how to answer the questions. If you live close enough for a ride-in fitting, it is worth the effort. Many of my friends ride a very long way (crossing many states) to arrange a ride-in fitting.
* Give your saddle some TLC. I admit that I don't apply that Leather Amore every month, but I am pretty good about applying it regularly, and it seems to have helped a lot. I try to keep the bike out of the sun, or at least cover the saddle and gauges with old towels.
I hope this helps!