The only reason to use a saddle pad with an ENGLISH saddle that fits your horse well (and the horse is fit with good topline muscle) is to keep the bottom of your saddle clean. When I bought a new Courbette recently, they recommended I ride without a pad for the first 10 rides, so the wool flocking inside would more quickly conform to my horse's back. She didn't seem to mind at all
. Now, that won't work if your saddle has foam or air inside, or if the wool is cheap synthetic wool.
Now, most horses aren't in tip-top shape and most saddles don't fit absolutely perfect, so it's best to ride with some kind of shock absorbing pad. I like ThinLine pads
. They do a great job of protecting the horse's back, eliminating pressure points, and even smoothing things out for the rider (they are recommended for people with back or hip pain). And they're thin enough that they won't cause the saddle to fit too tight, which thick gel and dense foam (like neoprene or that cashel stuff) can do. I use a plain thinline (the Contour pad) over a thin quilted pad. For shows, I use it under my show pad. For my western saddle, I use the 30x30 Western pad over a thin real wool felt liner pad. For shows, I put m nice woven blanket over the top of both.