Logically, the early 1960's style SG angel-wing pickguard not only looks better (why hide a nice grain & finish behind a big piece of plastic?), but it makes a better sounding instrument too. The PU's are mounted into the wood, making the vibration, tone, and sustain transfer more direct from the body to the PU.
With the big pickguard of the late 1960's SG's, the PU's are mounted into plastic, which is then acting as a soundboard, and that can't do much for tone quality. There's a sizeable 'middleman' between body & PU, and its pretty thin & flimsy. I expect Fenders to hide behind plastic, but a Gibson/Epiphone should show off its wood, for both cosmetic & tonal reasons. Makes sense?