Here's a few favourite buses I remember from when they were in service...
I never had a bad ride on an NBC standard ECW bodied Olympian. They always gave a smooth, comfortable ride, felt solidly built and in the summer they had enough well opening windows to give good ventilation.
I also liked the SYPTE Dennis Dominators, particularly the Fastline, dual-purpose examples. The ones Doncaster depot refurbished that ended up with moquette seating upstairs were wonderful, as the brown vinyl could be a challenge to stay in one place on with certain drivers!
For a single deck, I think an Alexander Strider bodied Volvo B10B wins for me. The ones I remember had double glazing, so you could always see out the windows! And they also had very tuneful gearboxes.
I won't enter the realms of favourite preserved buses, I have far too many!