I've thought about this, I have a Trevor James Horn Classic tenor and being a student model, it seems I'm better off sticking with this one- until somone more experienced tells me I'll benefit from a particular upgrade.
I have a Trevor James rev II and ditched the TJ mouthpiece very quickly on the advice of my teacher and have got a Selmer s80 C* which is much nicer. I am making a much better and more consistent sound since. I am coming up to the renewal time for my hired TJ alto and am contemplating what to do. Whether to keep it or go for something different. Haven't made that decision yet.
My son and I share a TJ Revolution Alto. When we first started he had a Yamaha 6C mouthpiece and I used the standard TJ. His sound was much better until I upgraded to a Meyer 5M. I use a Yamaha 5C tenor mouthpiece on my Walstein and find it very good for the price.