Unsure of heavy, my least played class. As for Scout, there's quite are few that are good. I wouldn't say Force-A-Nature or Soda Popper are really good, but Shortstop and normal Scattergun are pretty equal, just differently playstyles. All the secondary and melee weapons have their uses in different situations, too.
Spy has completely blurred lines, I wouldn't say there's a best for any slot. Normal revolver is all around awesome. Ambassador can destroy if you get good at aiming. L'etranger is amazing with the set, and a great way to snipe some people and build up cloak. Enforcer is all around awesome, but you have to be careful where you use it. Diamondback is the only one I'd recommend not using.
As for Spy Knives, again all of them are good in different situations. Big Earner slightly less useful, but still has its uses.
All the Spy watches are great too, none of them are bad.