Pistol whenever there is one.
Other times, like in Explosives or Chargeable, I use the Deatomizer.
Most noobs don't even use the Deatomizer in Explosives. When you snipe with a Deatomizer, you have enough time to snipe someone and avoid their rocket, while the other person has to stand still for like a second or two, making them an easy target.
I do it all the time and get massive streaks.