Just like Eimaj asked...it would depend on what rod it's going on to. The GPX is great for faster rods as it's about a half a line weight heavier to load those fast tips. I've tried the XPS on my 4wt, but I only liked it for dry fly fishing due to its very delicate presentation, but not for tossing long leaders in chironamid fishing.
If you dangle chironamids a lot, the two that I like right now are the RIO Nymph and Selective Trout tapers. I have the Selective Trout on my Winston BIIx 6wt, and the Nymph on my Winston IM6 4wt. I'm trying to decide which taper to go with on my 3wt, which is a pretty fast taper. I might even give that SA GPX a try.