Define "better".
Beta is BETTER quality, better built, smaller profile, better balanced...MGW is entirely plastic, lighter weight and hangs of to the side.
That being said, my 90 rounder has never failed me in a 3 gun match while I have seen Betas fail. I've been using it exclusivly for almost a year and load it to about 5o rounds to keep the weight centered. I'm a lefty and the mag hangs off the left side of the rifle so it really doesn't bother me, but it might enterfer with a right handers forward grip (the thing is large).
So for what I am using it for and the results I have gotten, the MGW is a BETTER value IMHO.
Picked mine up for $80, I think the Beta runs around $250? Its up to you if the Beta is worth the extra coin but the MGW flat out works.