There is good and bad in both seats.
I inherited a Corbin when I got my S4Rs, it was not to my liking. Very firm and low at the front.
No storage underneath as mentioned but I thought it was quite light.
I had a Sargent from my previous bike that I had kept and it went straight on the new bike.
It is softer has a nice raised hump at the front of the seat with the already mentioned storage tube (very handy)
The seat does get a bit heavy especially when you pack the tube full of bits'n'pieces.
My choice would always be the Sargent, you can buy direct from them. They are around $450-$600 I believe.
Buying a Corbin, I am not sure really haven't ever looked at them.
Then you could always look at the other option, the "Virgin's" seat but you might have to sell your first born to do so.
They are closer to $1000, enough to make your eyes