My first experience of 4 wheel railbuses was in Germany, and their ride quality was awful. Just as Germany was getting rid of 4 wheel coaching stock, BR inflicted the Pacers on us, and the riding qualities were just as bad; a big comedown from the Class 108s previously used around Liverpool & Manchester.
Yes - I know the 108s had to go - corrosion and/or asbestos, etc., but I wish BR had waited until something better than Pacers had been available.
Yes, I know the internal layout of 150s is awful, but for ride qualities alone, they were always preferable to any Pacer.
My favourite 2nd generation units were 156s - the only improvement would have been sliding ventilators where passengers could control how far they opened. Hopper ventilators are diabolical - either fully open - and a howling gale, or fully closed and you get overheated on hot summer days. They mostly had good legspace, but some refurbs seem to have got worse.