Would like to know the same.
Haven't attempted a LONG ride yet, for exactly this [sore butt] reason.
To start, their is not going to be much padding on a seat for a NINJA. But, I have done some reading / research on both Saddleman and Corbin. I think that if I was making a choice right now, I would most likely opt for the Saddleman. One reason being is that the shape is somewhat different. Different in a way that it provides more area for your butt cheeks.
And the front of the seat is angled differently than a stock seat as it provides some resistance from sliding forward into the gas tank.
With that said, I opted for and installed the " Kawasaki Factory GEL Seat " on my NINJA. Only have about 300 miles on it and can not provide a full review. But it is somewhat more comfortable than the stock seat and after a period of time it does seem to be taking the shape of your butt.
One thing you do have to take into account as with the factory GEL seat, it is " ONE " inch thicker than the stock seat. Not that you will notice it because you are sitting more into the seat, but you are sitting higher and thus you are reaching more forward for the handle bars. And if you are on the short side with a short inseam, you will be reaching further to touch the ground.
As for comfort rides on the NINJA, " PERSONALLY " I feel that a 100 mile break and stretch is a requirement. It seemed to work for me when I had the stock seat and I am still doing so with the GEL seat.
But in closing, I think that if I had to do it all over again, I may have opted for the Saddleman seat. But before you opt for it, their is one other thing I would check out and that is the PASSENGER PAD. The factory seat comes with a new full GEL matching passenger pad, while I think some of the other seats mentioned only come with a passenger pad cover.
Just do your homework and good luck.
P.S. If you are looking for real comfort, then buy a Honda Gold Wing