I am a huge fan of Modified Association trees in western saddles. They are most often seen on Ranch type saddles and they have a deeper seat and larger swells for more security. They also have a very secure pocket for you to sit in that keeps you comfy and secure throughout the entire ride.
This is mine that was made custom for me by the Corriente Saddle Company. I've been using it on all my horses since I got it and haven't had one come up sore yet. And, one of the best things about it is that it was exactly what I wanted for less than $700.