I've liked HSTs since I can remember, and I try to plan any trips from Birmingham - South West/North East around XC's timetable.
However, I think it does depend on which refurbishment you get - whilst not strictly HSTs, I thought the Virgin West Coast one was best (especially in 1st), Virgin XC, Midland Mainline, FGW (older one) and GNER (both) were OK, and FGW new one is pretty dire.
That said, HSTs do have their downside - they don't seem to be as reliable (at least, I've had two HSTs break down with me on board and another run 90 mins late due to a breakdown), although that might just be my luck.
It was quite nice to see though, when I was travelling back from a holiday in Cornwall (on a Mallard hire-in), I told one of the less railway-knowledgeable people travelling with us that we were on an InterCity125 and he was very shocked, and couldn't believe they could seem to good - he thought it was a new train.
The same happened when I travelled on the VWC hire-in set, people everywhere were exclaiming how much nicer it felt - mind you, they weren't so happy when we ended up about 15 minutes late at Birmingham...