Just FYI, there is a which gun section >.<
But anyways...
Either the Ion XE or the Epiphany IMO
The REDZ Ion isn't the greatest, it only comes with a new body kit, clamping feedneck, PepperStick (great barrel though), and a REDZ bolt (not the best), and I think it also comes with a REDZ Ion trigger.
I'd get the Ion XE over the REDZ Ion because if the BOB feature, making it worlds easier to clean, and after that, you can do the stock bolt mod and make it just about the same as a REDZ bolt, but for free!
I'd get the Epiphany over the REDZ Ion because of the higher operation pressure, and because of the volume control inserts. With the Epiphany, you will never encounter shoot-down, and with a FRAEK Jr. as the stock barrel system, all you would have to do is get a FREAK BoreMaster Kit and you're good to go. A BOB body would also be something to look into for the Epiphany.