You would not go wrong with either guitar.
The Epiphone is likely less costly. I can't remember if the Pacifica is "chambered"...if not the Epi will be lighter.
Some folks say this impairs sound quality. But my rule of thumb is, if an electric guitar sounds good unplugged, it will sound good amplified, unless the pickups are total crap.
If that's the case, another hundred bucks will put an awesome set of Seymour Duncans in that axe.
I have a very old Tiesco that sounds pretty good unplugged. It has pick-ups that are "microphonic" (by design) and even though they tend to gather a lot of background noise, they sound pretty good.
It'll come down to what kind of music you intend to play with it. The SG is more of a rocker, the Pacifica tries to be more of a "Jack of all trades". If my memory serves the Pacifica has single coils and the SG has humbuckers.
The 'Buckers will be louder, and they will also not buzz in the presence of flourescent lights. If you get the SG with a "coil-tap" it will allow you to go single coil when you want to wail "strat-style", but you can go back to "les paul style" with a simple push of the coil tap knob.