Mark V Delta and EOD for sure. I love that Mark V Delta is based on the one that featured in Halo 3 since that's my favorite rendition of the helmet. Mark V Alpha looks like a damn chipmunk, so it's about time.
I often used Security in Reach, and I'm glad to see the return of the ol' Recon style. The only thing that could make this update any better is if we had more customization options for our Spartans.