185s.
The original seats were dreadful pre-refurb, ride quality is poor, noisy, fairly cramped.
Supposed to be 4 car units, always been plagued with overcrowding issues as a combination of the 3 cars, and poor utilisation of the space: only really 2 coaches worth of standard class seats, nowhere near enough luggage space, no proper cycle storage (exascerbated by not being allowed to keep a bike in the area between first and the accessible toilet).
As a 158 replacement they were a downgrade, I always thought.
15x 'refurbishment' is offensively bad.
Growing up between Manchester and south London, 455s were a disappointing replacement for the slam doors (especially seeing other lines get Electrostars), and my first introduction to ironing boards.
175s, if they were reliable and all 3 car they'd be really quite nice.
CAF units, the cheapness is clear. I don't often ride them but when I do I'm always alarmed how quickly they're wearing.