Ilovestitch- I looked at that pad, I was worried that with it being neoprene it would be very hot on the sides and irritate the horse. I didn't think it would breath except down the middle where the holes are.
I love it actually! My horse seems to be alot more relaxed on trails with it too, I can switch between that pad and my other felt pad and it makes a big difference. I have been using the pad for over 2 years now and have ridden as long as an all day trail ride while camping and he has never had any irritation.
Western pads I prefer cut-back (not built-up ones though) because they just give an extra bit of clearence and eliminate worries that there would be any wither pressure, which can happen on long rides with a standard pad, even when you make a big clearence they still sometimes slip.
For trails, and just for riding I use my Theraflex pad. I was very nervous about buying one as they are pricey, but it has made a world of difference to my horse. It not only keeps the saddle in place most of the time (as much as a saddle pad can do), but it also is breathable, and fills in any weakness to the topline that my horses may have. I have both the western and the english one (I rarely ride English anymore, but I still have my english saddle and my english saddle pad).
I highly recommend the theraflex pad, I will never ride without one now they are amazing!