Another factor is how upright (or not) your riding position is. I've found that, if you are on a road-oriented saddle and riding more upright, it will be hard on your butt. If your pelvis is rotated forward by your being more horizontal, the road-type saddle will feel 'right'. The converse can also be true. If you have a seat designed for an upright position (wide and soft), it won't allow you to ride comfortably in a more horizontal position. Some seats are designed for you to ride "in" them; others are designed for you to ride "on" them. Some allow you to move fore and aft, others do not. Some are curved and allow the seat to nestle in between your cheeks; others are flatter and wider, so your bones rest on the wings and you stay on top of the seat. I just switched to one of the latter (160mm Bontrager)... feels great when riding, but leaves me a little sore. I expect that to go away, but(t) if it doesn't, I'll find something similar with a touch more padding.

You need to find a seat that not only matches your body, but(t) also your riding style.