For Historical, I'll say the USS Constitution as a prime example of the era.
Runner-up - The Bismarck
For Current Day, I'll say a Navy Aegis Destroyer like the McCain. Not just because our work here supports them, but because Missile Interception is the absolute future of surface and space warfare, and these vessels are key to perfecting it.
For Fiction, and saying pure warship, I'll go with the classic Klingon D7 - both as a model I used to have and loved, and an iconic look that perfectly captured the menace of the race that came with the ship. The Command Boom idea is probably as dumb at the Federation Bridge "Bullseye" placement, but it just looks cool. All the modern versions (Bird of Prey, Romulan D'Deridex, etc) all ape that original look.
Runner-Up to the possibly non-Military CYGNUS from THE BLACK HOLE. Also a model I had for a long time, and the first example of a "cathedral" ship that I recall (for me at least it predate the Nostromo). Such a great look when they first find it, a void against the void, all outlined spires in the light of the titular accretion disk. And then it illuminates from within with that blue light ... SO cool
Worst Ship Designs that I'm Still Stupidly Fond of:
-- The Eagles from SPACE 1999
-- The Liberator from BLAKE'S SEVEN
-- and of course, Serenity