Well, I'm sure I spend too much time on here having a dig at Pacers, but as the gauntlet has been thrown down I'm afraid I just can't resist having another. This is mainly because out of the vast number of train types I've commuted on (including 150's, 158's, occasionally Mk 4's, Mk 3's and of course, Mk 1 slammers) Pacers are by far the worst most cramped, cheap and nasty uncomfortable trains I have to travel on.
With regard to the Mk 1 DMU's, I grew up in Kent so my experience of diesel traction was mainly of Thumpers dating back to the 1950's and 60's (and travelling on these was generally an ecstacy of pleasure in comparison to Pacer travel). I did, however, occasionally travel on some very long-in-the-tooth 1st generation Western Region DMU's which ran between Redhill and Tonbridge in the early nineties, and whilst they did seem rather basic in terms of passenger comfort, there weren't any noticable problems with regard to ride, smells, noise etc and certainly nothing worse than a Pacer unit today. I have also travelled more recently on similar units on preserved railways which has generally re-enforced my impression that the Pacers did not represent any sort of improvement at the time other than not suffering from problems associated with old age/lack of maintenance etc. That said, my experience was limited and there were probably a lot of poorly maintained life expired examples on the wider network at the time.
Perhaps if BR had decided to replace the first generation DMU's more gradually with better rolling stock instead of trying to do too much in one go, we might not now be lumbered with a large fleet of sub-standard trains with little prospect of replacement in the near future.