ORIGINAL: TulliusDetritus
I might be utterly wrong but I think it's better to aim at Harper's Ferry [:)]
My reasoning: even if you capture Manassas the Confederacy can easily recapture it, I think. And you will have lost an opportunity to grab the first stone in the Valley (HF).
If you succeed and take HF (and the Confederacy almost cannot stop you), you force them to divert forces to the Valley or you might take the next stone (Winchester) and then the last stone (Strasburg).
Therefore IMHO HF (in fact the valley) is more important.
That's how I see it [8D]
if you capture and convert Manassas to Union control, the Mac events don't fire, and you save 10NM. Can't do that in CW2 unless the Rebel is asleep.
(Yes, in my current PBEM, I took HF. And yep, I have an opponent who doesn't care for the "everything east" game killer.)
The way it stands, since PGT's army forms in Manassas, HF is the better move. (If you don't rail, they go through Leesburg, so you get that too.)