First off I would say, if it's matted so badly that you can't comb some of them out. Then clip off the really bad matts yourself, or take him to a vet/groomer to get it done.
If you take the time to groom your long haired cat everyday, just about any type of brush will work.
I have a metal slicker brush, and a metal flea comb, between the two I never have any problems with matting.
Don't comb your cats hair while it's wet, that can make the matting worse, you can comb it before or after a bath (once the cat has dried a little.) If your trying to comb out matts, do it just like human hair, start at the ends and work your way inwards towards the skin. Some matts you might even be able to work apart with just your fingers.