Having ridden XC's HST sets twice now I find them excellent - they're airy, well furnished, and the seats are comfortable.
GWR's are far more claustrophobic in their style, with higher backed seating and harsher white lights fitted. Personally far prefer the XC sets, and when you get a HST as opposed to a Voyager, it is a far better experience.
What is wrong with CrossCountry anyway? My dad travelled on an XC 170 from Audley End to Birmingham (just over 3 hours) once and he really liked it! Their colour scheme is pretty good too!
Only real issue with Cross Country is the lack of capacity on the Voyagers, which was not XC's fault in the first place. If XC had the additional units, or carriages, to strengthen the core services then there wouldn't be much wrong. The routes the 170s work tend to operate more smoothly in my experience, and at least the 170s have had a refresh. I find the customer service very good - the train staff usually helpful and attentive, and the delay repay system works well there in the two times I've had to use it. Basically, give it some capacity boosting investment and it would be a better franchise. Welcome to the forum by the way Ayman!