The Epiphone Les Paul custom has a much better tone and all around more quality. But the standard and studio have more of a heavy tone making them great rhythm guitars. I recommend a Gibson standard or studio, they will give you more quality than the epiphone, but the custom will beat them all plus the price is great.
I'm sorry, but you hae no idea what your talking about regarding Epiphones. The studio, standard, and custom are all the same, on the inside, same pots, same caps, same pickups, same tuners, same bridge and hardware. The differences lie in the inlays and purling and binding, a studio should sound exactly the same as a custom, It just won't look as nice.
Studio: Plastic dot inlays, no binding, plain finish.
Standard: Better top, Pearl trapezoid inlays, and body binding.
Custom: Same top as the standard, Supposedly uses mahogony, but instances of use of Agathis, which is a cheap alternative to mahogany for the body, has been reported in many 07' to 09' customs. Has Body and neck binding, as well as headstock binding and body and headstock purling. Pearl block inlays and an ebony fretboard. Also has gold hardware.
As I said, the Custom will solely look better than the other two models, but sound will be exactly the same, due to same hardware/electronics.