It really depends on where you want to hit the rack. You always want to hit a ball in the rack solid and not to much to the lower side or higher side of the intended strike point, or you don't want to hit the "crotch" as some would say. Your best yield will result from hitting the intended ball in the rack solid. So there are times when a follow will not get you there, and times draw will not get you there.
In general though, what I like to do is if its a backcut breakshot I like to follow. If the breakshot is not a backcut I like to draw, but there are exceptions to that if I can't hit my intended spot. For instance if the tangent line with the follow shot is leading me into a "crotch" then most likely a scratch is in order. I will then draw to hit a ball solid to get away from the scratch possibility.
Another exception is if you can only hit the lower corner ball, most the time from wherever I am with the cue ball I like to follow that shot if possible.