Depending on availability, you can sometimes see 175s be relegated to Ebbw Vale stoppers and Cheltenham to Maesteg trains while 158s and even 150s work the West Wales- Manchester/ Holyhead services. However this is pretty uncommon and the majority of the time it isn't the case.
I suppose if you're travelling on the Aberdeen- Edinburgh or Highland Main line, you'd much rather travel on a short formed ScotRail HST than an Azuma or a XC Voyager, I know I would. Going by the same logic passengers in Cornwall, Devon and the West of England would probably prefer the local services provided by Castle HSTs to the Class 800/802s on the London expresses or the XC Voyagers.
If you're travelling from Birmingham- Shrewsbury I would assume most prefer the West Midlands 170s to the TfW 158s that travel beyond Shrewsbury to North Wales and Aberystwyth.
If I was travelling from Southampton- Portsmouth I'd sooner travel on a local 450 than a Class 165 or 166, or even a 158. It's not unheard of for 150s to work the route, so I'd definitely take a 450 if that was the case!
I would also agree with the 390 Vs 350 situation on the WCML, I don't mind short journeys on Pendolinos, but most of my long distance journeys on them have been miserable. There's just something stuffy and claustrophobic about them. Meanwhile I'll happily travel on 2+ hour long journey on a 350, they're surprisingly comfortable, and seeing as they can do 110mph they don't feel much slower than the 390s. Nowadays when I travel from Manchester to London I always opt to change at Crewe to the 350 on the semi fast service to Euston. It's definitely slower, but it's cheaper and I find it to be much more comfortable.
These are all the ones I can think of for the time being. Of course, what defines a train as being "better" is mostly subjective, so everyone's opinion is likely to be different.