I'm not particuarly fond of the standard class seats on 'Mallard' refurbished HST's it feels like im going to slide off.
I'm glad to find I'm not the only one who finds the "Mallard" seats very uncomfortable!
With me, it's the fact the seat is one-piece, with a moulded curve where you'd normally have a cushion and seat back.
My spine just doesn't fit this curve, and after a journey from Leeds to Kings Cross and back recently, I had very painful sciatica the following day.
The first class seats on "Gerald" from North Wales to Cardiff are similarly-shaped, and on the odd occasions Mrs W and I have treated ourselves to breakfast/dinner on that train, I've had to keep getting-up and walking around.
Which does little to aid the digestion!