Why not just keep both? They both have unique features and uses, and both are great machines. They take up minimal space, and unless you need the money, there doesn't seem to be any real reason to sell one. I would sit on it and see what you are using over the next 3 months. If you find there is one machine you don't use any more, and have no particular attachment to it, then that is the one that should go. But I'd just hang onto it if it were me.
//e, //c, IIGS, 128K, 512K, 2 x ED, Plus, boxed SE, SE FDHD, SE/30, Portable, CC, Performa 250, boxed LC, boxed Quadra 700, boxed PM6100, TAM x 2, boxed G4 Cube, G4 iMac, TechStep, TC, ATV, 15" Mid-2012 i7 MBP, 27" Thunderbolt Display, iPhone 4S