2x will be the easiest to get used to, but a 4x will obviously do more magnifying. A 6x outdoors is really unnecessarry and actually said to be worse b/c of too much power. 6x is good for spots, but will blurr a 3d target. It is sometimes hard to find the circles on 3d targets as well with the 4x but you can get used to it easily. 4x is what is typically used for 3d.
Derek