GD,

Greaser's definitions are spot on. In my experience, running at lower magnifications, I would go with a FFP scope, reason being: FFP scopes have a tendency to obscure the target at higher magnifications (it's often perceived that way, anyways). At a lower magnification (I've used them up to 10x and loved them), it will allow you to dial in your dope without having to add another factor to the equation, which is at the least more work, and at worst allows for yet another error to throw the shot. You can't miss fast enough to win a gunfight. (raccoons, you'll probably live another day, though.)

-however-

In my experience, if you run a higher magnification that 10x, an FFP becomes unwieldy, while the SFP optic continues to offer a finer aiming point at any magnification. I can't recall seeing a FFP optic with more power than 12x, but I don't research optics as often as other things. I'm sure they exist. Anyway, the Wally World special I was running on my M14 ran up to 16x, and is a SFP optic. The subtensions for the reticle were calibrated at 10x, so around that magnification my dope was usually on (there was no detent, so it was impossible to get it exactly at 10x.) They both have their pros and cons, but IMO they each fill a certain niche better than the other.

Ultimately though, try before you buy if you can, nothing beats firsthand experience when it comes to equipment