Well, as a soldier I've probably got a 50:50 kill rate with spys. They end up killing me as much as I do them being that the soldier is the 2nd slowest class. I spy check a lot so I end up killing them without knowing it (until they blow up) most of the time. Not as an engie though. Once the sentry is up I'm plugging away with the shotgun at everyone that even gets close to me. Three good shots with a shotgun will usually kill a spy. Then there's still plenty of time to get the sapper off the sentry. I sometimes loose a dispenser in the process though.

As engie I get killed by those damn demo's and a heavy medic uber combo the most. Everyone else, including pyros, I usually take out pretty easy.