The best branch of WH Smith & Son is, undoubtedly that in Newtown, Powys. It also contains the WH Smith museum.
Euston's is the most historic but is merely a part of that ghastly station's oh so dated concourse.
My most regularly visited branch of Smiths is at London Victoria, and I have a penchant for buying magazines there associated with the many former hobbies I've had in years gone by. These I then leave about the house on my return home so that the lovely Helen understands that she's getting off lightly with just the cycling, bass playing and longboarding these days, the latter two of which I never buy magazines about.
Smiths as a bookshop though? Outside of airports, no. No. and NO.
And if you are shopping in Menzies you're shopping in Smiths, surely?