Counterpoint: I played since a month after Vanilla launched until about half-way through WoD.
By your logic I should be a hardcore "Vanilla was the best" player, but actually, I'd argue that most of the game peaked in TBC (the first expansion) and raiding peaked in Wrath.
MMORPGs was always about grind-to-win, ideally forcing a group play along the way - that built communities.
Blizzard kinda killed that turning the game into a solo adventure - most people just logged in for a raid and be gone for the rest of the week and those casual pug raids was the last nail into the coffin of social bit, that actually kept me playing.
I've had enough in Cataclysm, but I can't really say if vanilla, tbc or lk was the best (ignoring my personal achievements in each of those, tbc was the peak of my raiding). All of those bring good memories.
By your logic I should be a hardcore "Vanilla was the best" player, but actually, I'd argue that most of the game peaked in TBC (the first expansion) and raiding peaked in Wrath.