i own several ions and an epiphany. The epiphany frame is a delight, but other than that I would say go with en up'd ion.
below is my current setup. The only thing left from an epiphany on it is the frame, grips and freak barrel (and breach, but that is the same as the one on the ion).
I have gotten several (up'd) ions and an epiphany and taken the best bits and parts from different ones and this is what I have:
(just the other day I ordered a BOB body for it. after that I won't do anything to it unless it breaks)
a word of advice, the ion and epiphany frame have different size holes for their triggers (the epiphany is one size bigger, meaning that the screws from an ion trigger will not thread). Also, the firing can on the epiphany (where the inserts go) is a bit narrower than the stock ion so you can't use the orange nano bolt upgrade kit with an epiphany can.