I prefer Dark Pit in customs.
The Electroarm is automatically much better in customs due to the Guiding Bow. You'll be knocking people off stage more than regular Pit, which puts those Guiding Bows to great use for gimping and controlling landings, which can lead to early kills.
Pit can't knock opponents to the side without the Uppercut Arm (I think)--y'no, the one that's supposed to be really fast but has so much start-up lag that it's not even faster than the original? Yeah, that one. But it sucks, so it's not worth equipping.
Think it's an awesome advantage and gives Dark Pit more options than regular Pit.