A= Origional BREL Class 158 Seating, Northern Re Cushioned theese seats with thicker foam to meet new regulations as did SWT But Foam Padding wasn't as thick most 158 operators have done this.
C=Richmond Seating this is the first time Ive seen them fitted into a 158 most common in ex ANE 156 Units.
D=Chapman Seating I here alot of peple slagging theese of but personaly I find them quite decent.
I think only EMT have gone for compleatly new seats with there Internal Refurbishment as most othe r TOCs have just refreshed the Interiors Norther only do the very very BAsic Capret and Seats and a bit of paint here and there if that sometimes.
Richmond was until recently on all of Scotrails 158's (bloody uncomfortable for me as well). 158701 - 158724 have been refurbished with new seats (Grammar same as EMT's). 158725 - 178741 have had the Richmonds recovered (the Grant from the Highlands didn't cover this).
The Richmond seats from 158701 - 158724 were recovered and sent down South to FGW hence why they are in their units.
In Scotland you can find every seat possible fitted into a 158 in thier patch.
You have the new seats 158701 - 158724
You have Richmonds 158725 - 158741
You have the original but repadded 158786 & 789 (there is also an ex-CT unit but can't remember its number you can tell it as it still has purple covers - or did when I was last on it)
You have the Chapmans 158868-870?
Having travelled on them all my personal preference is
Grammer, Original, Chapman, Richmond