I'd have to agree with the majority of posters in that the HST/Class 43/Classes 253 & 254 must win the title.
- Designed as a low(ish) cost stop-gap until the APT could be made to work
- Designed to operate within existing signalling constraints at 125mph
- Best-riding coaching stock ever on BR
- Dual unit reliability so that if one power car failed you still had a fighting chance of getting home
- Doesn't smell of toilets
- Sound great
OK so they had a few reliability problems in the beginning because the radiators couldn't cope with hot weather, but when the final history of the great trains is written, they'll be up there at the top
I think it depends if you are looking at it from a TOC view, a passengers view, or an enthusiast's view, what is "best"? HSTs are good for TOCs, but I would suspect most passengers would prefer a nice quiet, fast, EMU to travel in. On ECML the 225 is far nicer to travel in than the old fashioned HSTs.
A question, is the HST considered great because it really is that good. Or is it great by default, as it had to last by necessity, because of a lack of investment in newer designs?
I do however think it is quite sad, that possible the best train designed in UK, is more than 30 years old, very noisy for people who live near the tracks, slow (compared to a TGV say) and obsolete compared to current European standards of passenger comfort and safety design.
Alas it says a lot about UK railways and UK manufacturing! Very sad considering we once led the world in railways.
My vote (if talking about the best class actually designed in the UK) goes to the Class 91, pulling a rake of Mk4 carriages. It had quite a few interesting features, such as allowing the 91s to be used as freight locos, body mounted motors to reduce track wear at high speed, state-of-the-art computer-based electronics for power and brake control, was the most powerful UK built loco until the Class 92 came out, and still (I belive) holds the British loco speed record. It was BR's last really great moment (I believe the Class 91 loco was even delivered on time, in 1988 after only 2 years of work, following the signing of the contract), and its a train that I would be much more proud of showing to someone from abroad, who knew nothing about our railways, than an old HST.
But I supose that is all down to how I define "best" class design ever, define "best" differently, and it could be an HST I supose! I would point out I think of best, as up to date, at the forefront of technology.
If its the best all round class opearting today in the UK, I would go for the Desiro, a very flexable design, again with great technology, with a lot of good safety features too.
Best train operating in Europe, then the TGV Duplex, full of innovations, and right at the forefront of current train(with wheels) technology.