Well, how about neither? That's helpful I'm sure.
For the type of shooting you're going to do, and the type of gun is going to be on, I would seriously consider a red dot sight like an Aimpoint PRO. Targets still seem pretty small at 100 yards with a 3x, but with a red dot at least you get speed and both eyes open capabilities. A 3x scope isn't very versatile, in my opinion.
Variable power scopes are more useful for hunting type rifles, in my opinion, because hunting allows more time.