I bought a used Gibson Explorer about 3-4 months ago. Its an '89 ... black with white pickguard. The neck plays very nicely, and the whole guitar screams. The previous owner bought it new in '89, and he installed some Duncan Invader pickups into to it. They have a higher output than the stock pickups. I stole the thing ... paid $600 for it.
I would say, buy whichever one you can afford. Like Muad said before, Epiphones are made in an overall "cheaper" way. So I wouldn't imagine the resale for a used Epiphone is going to be as high as the resale price you could get for a true Gibson. If you can, I would say hold out for a true Gibson ... but no matter what, get the guitar in your hands and listen to it before you buy it. You may find a really nice sounding Epiphone that is well-worth the money. Just get your hands on as many as you can and buy the one that feels the best to you.