Re: what scope is best for a .243
If you are thinking of shooting LR, you'll want to go with the heavier, higher BC bullets. To shoot those out of your rifle, you'll need to know the twist rate of the barrel and make sure the bullet weight you have will be stabilized by the twist. Example: I am shooting the 105 AMAX in my .243 Win competition rifle and pushing those bullets out to beyond 1K. Twist rate is 1:8 to properly stabilize the bullets. Heavier than that and most people will recommend a 7.5 to 7.7 twist.
So first, figure if you have a rifle capable of shooting to the LR that you would like to do. After that, I'd recommend a scope in the 3-15 range for an all around magnification range, preferably in FFP but that isn't an absolute must have.