Ahhh, we had this discussion a little while back, it's so buried that I was too lazy to try to dig it up. Anyway, both kits have their respective pros and cons. I built the Academy one and liked it. Very good fit, good overall appearence.
I don't know too much about the AFV kit other than that it supplies a metal barrel w/recoil spring. Academy's is the two part plastic type. Verlinden makes the aftermarket update kit for the Academy, while this could be used with the AFV kit.
Here are some reviews by others more qualified than I:
AFV's kit
http://www.argo.net.au/jbwhole/reviews/afv35015.htmVerlinden's update set for Academy's kit:
http://pmms.webace.com.au/reviews/vehicles/v1512.htmAcademy's kit:
http://members.tripod.com/TheBunker_/m18.html