I've just ordered some XR's for a couple of new touring bikes (so my comments are just based on research not experience). My dealer was pushing Pluses for puncture resistance but their weight is an issue - 980g for a 26 x 1.75 vs 790g for 26 x 2.00 XRs -- or you might prefer the 26 x 1.60 XRs for lower rolling resistance, they're only 595g - big difference. This seems to be because the Plus's puncture resistance comes from a thick layer of rubber whereas the XRs use a thin Kevlar-like fabric. For a rave about how heavy the Pluses are see
http://www.crazyguyonabike.com/forum..._id=100499&v=4

I phoned the Schwalbe distributors here in Australia and they assure me the XRs really are just as puncture-proof and durable as the Pluses. Schwalbe gives both these tyres their maximum six bar rating on puncture resistance and durability.

Another factor is that the XRs are available as folding tyres, the Pluses are wired only - trickier for spares.

I'm positively itching to try out the XRs ... and the new bikes