For Soldier, its a toss up between the Drill Hat, and Lumbricious Lid. Sometimes I question why I have both a Vintage Drill, and the Lid, as the Lid usually gets more use (because of dat Holy Handgrenade taunt)
For Spy...
I like my N&B Fez, and give zero shits about those who call it "Cancer" as my IRL job is mechanical related, more or less. (I used to be an auto mechanic, but now I do stuff more on the technical side).
Plus, as far as Spy unusuals go, I kinda like nice hats with effects that you can't pick up all the way across the map (smoking, N&B, Confetti, Massed Flies, etc)
Sansnar's Detective Noir collection is pretty baller, though.