i ride on both sorts of traction regularly
So do: I travel from Barnstaple to Leeds regularly, and find that I can sit comfortably in a Voyager seat, as there is enough room between me and the seat in front (which is not true of Pacers), don't get backache as the seat has been properly designed (which is not true of Pacers), can work at a table (of which there aren't any in Pacers) or - where necessary - using the fold-down tables (of which there aren't any in Pacers), and can charge my laptop in the power point (of which there aren't any in Pacers).
In addition, if on the poorly-maintained jointed track we have to put up with between Barnstaple and Exeter I wouldn't have to brace myself to avoid being thrown to the floor (which I do in a Pacer), I don't go deaf from the incessant noise coming from the wheels every time they hit a joint (which I do in a Pacer), and if I'm with someone I don't have to shout to make myself heard (like I do on a Pacer).
Plus if I'm hungry I can walk to the buffet (which I can't in a Pacer), and I can get in and out of the toilet without any circus training (which is tricky in a Pacer, and is downright dangerous if it hits a bad joint while I'm in there).
Finally, heaven forbid that I'm ever involved in any sort of rail accident, but if I do I want to be in a Voyager when it happens, as I will have an immeasurably greater chance of walking away from it unscathed.
Pacers are cheap, nasty, uncomfortable and unpleasant. Voyagers are much, much better.
you can slouch on the bus seats
They're not bus seats - buses have far nicer ones...