Sydney Sleeper, while not even a sniper rifle (Ayyy) can actually be somewhat decent with offensive, as it gives minicrits (Critical with the Bushwacka)and can instant kill when fully charged,but I don't like it very much (Hitman Heatmaker so much better)
Flare Gun is really good, I either main that or the Scorch Shot for Pyro, plus CRITS
Bonk! Atomic Punch is good for drawing enemy fire at you for distractions, plus you can use it for getaways or, in the cases like CTF, you can move through the enemies to get closer to the briefcase
Crita Cola I don't use, the Atomic Punch/Mad Milk or any of the pistols would be better
I also don't use the Southern Hospitality, but it can be useful for tracking down spies with the bleed effect.
Eyelander, when playing as a 'Demo Knight' is good, I use it along with the Tide turner and the Greande Launcher
Family Business is good for Heavy as it shoots faster than the normal Minigun and can be used faster as well, thanks to the lack of spin-up time, but I use the Sandvich instead
Crusaders Crossbow is good for healing teammates when they're far away, plus it's more accurate than the normal Syringe Gun, though I like the Blutsauger more