I'll throw in a vote for attending the actual school in Quantico. I just graduated this summer and it was truely a b!tch! But, there's no substitute for getting in amongst your peers from all over the MAGTF and learning a thing or three from them. Toss in a bunch of International Military Officers and reps from every other branch of the US military and you've got a legit school. I'll highly recommend it to everyone I run across for the remainder of my career; it was THAT good of an experience.
I've been told by many to go ahead and do the correspondence EWS, but be sure to do higher PME in residence. The reasoning being to stay out of the FMF for as short a period as possible as a company grade officer. Is that a legitimate concern? Did you do it in conjunction with a B billet in Quantico?