Had a trip to Cheltenham on the weekend and was delighted to get a HST on the way there - so big and roomy and comfortable and quiet - and then the opposite of delighted to get a Voyager on the way back. Cramped, rattly, beaten up and tired, the PIS didn't work, the reservations didn't work, the internal door in the carriage I was in barely worked, the vestibule stunk...
I do think it's mostly the internal "spec" of the Voyagers that's the problem, and the CrossCountry ones are notably worse than the Avanti ones, but they're my least favourite train to travel on. The fact that I have had far too many journeys on the Birmingham - Manchester service which were rammed to the gills, and for which they are clearly, totally, ridiculously unsuitable doesn't help matters.