I also agree that it is partly what and how you ride. When I'm buying a saddle, I want to make sure first and formost that it's going to actually "fit" my horse's back as well as possible. I could name several friends/fellow horse lovers, including myself that has had problems in the past with saddle fitting. It's NOT fun to you or the horse if you end up with a poorly fitting saddle that makes your horse sore and hate your guts for buying him a saddle in the first place! (I've been there)
If I'm trail riding for a good handful of miles, training (first saddled horses), or swimming horseback, I like a nylon saddle (though I don't know of anyone's having luck with the cheaply made ones). True they are lightweight, and easy to clean.
For just about any other purpose, I prefer a good made leather saddle.