I like to backstab Razorback Snipers just to see if I can get away with it. Maybe 40% of the time, I do.
My favorite weapon is the Homewrecker; Seeing an enemy Engineer haul and deploy his level 3 sentry, then rushing in like a madman while it constructs and trying to break it is.. Nowhere near as frequently useful a tactic as those made possible by the Axtinguisher, Powerjack or Backscratcher, but it's hell of a lot more entertaining. Well, the whole sapper removal thing occasionally comes in handy, too, but the bumrushing is really my main reason for using it.
My least favorite is probably the Machina. It encourages bodyshots, is one of the most visually unfitting weapons in the game, and it shoots obnoxious-looking tracers.
Also.. Silver815, why the poop do you use the Backburner with the Axtinguisher? They have terrible synergy; The BB's bonus is made redundant by the Axtinguisher, essentially making it a nerfed Stock Flamethrower. The Degreaser, on the other hand, is practically tailor-made to work well with the Axtinguisher.