On the main line, Another vote for Lewes. Especially considering that some stations either side of Brighton look like they are from Eastern Europe, and the first thing that greets you at Seaford is a vending machine with no insides... The only thing that mars it is an irrational feeling you might sink into the gravel that's been used to fill in the bay.
For larger stations, Brighton itself gets a vote, only marred by the fact passengers have been turned out of the waiting & refreshment rooms to be shat on by pigeons in the main concourse.
Ones I've not been to .. Great Malvern gets a vote,
Penhelig looks like somewhere in Japan.. a bit.
Cambus o'May looks like nothing else except where you'd get off for the Dangerous school for Wizards.. but half a vote for not actually a station.
On heritage lines, Horstead Keynes, Corfe Castle and Minehead in rough order. On the smaller side of heritage lines Medstead and Four Marks esp. If the signal box is still in situ and all the activity can therefore be seen and heard from right by you as a train threatens...
Off topic, for modernity and efficiency Reading is probably an exellent example, although that awkward kink in passenger flow on the south side might be more obvious during peak hours..
Way off topic, platform 1 at Salisbury looks as though it is inching forward to being brought into use. The only thing missing would seem to be the digital information boards, and most likely the most expensive part being the signalling , which I suspect might be part of that. Meanwhile the coffee and panin outlet on platform 4 had been turned into something similar to a shop on a garage forecourt ...