I use neoprene and mohair. It doesn't matter so much if you buy high quality. Keep in mind, a lot of this depends on what you want to do. But for trail riding, unless your horse has a specific issue, either physical or behavioral, then the material of the girth is not as important as making sure it's clean and fits properly.
For saddle pads, I use foam or wool. Not the fake wool, but the real stuff. I don't use felt at all. I've found that felt retains too much heat over the horse's back. My foam pads are about 3/4 inch thick. My wool pads are a little thicker. The genuine, high quality wool does let the heat dissipate much more easily than the felt pads. I would recommend investing in a high quality saddle pad, no matter which type you decide on.
Well, I guess I would recommend investing in high quality tack, period, and maintaining it well. If you choose wisely, it lasts for years.