I keep going back and forth. I still have good u4/3 glass and shoot the GH3, though mostly video. I was about to pull the trigger on the EM1 but held off. It feels a bit better in my hands than the A7, and my head says EM1 since I've got a good set of lenses (12-35/2.8, 35-100/2.8, 25/1.4, 45/1.8) and also the GM1 which is a fun little camera. My head says that staying in the same "family" gives the most bang for the buck, and the touchscreen on the EM1 makes for quicker shooting and the IBIS solves a lot of issues in low light and for run-and-gun video. I find the IBIS works better than the Panny OIS.
Plus I've never quite gotten on with Sony, and have somewhat of a bias about the company. Not sure why, but brands are funny that way. That said, when I look through the various forums here I see spectacular shots with any of the systems (since the shooters are *very* good), but for some reason the ones in this thread seem to stand out. I do have a 135/2 L lens that I'm not using that could go away and make up the difference between them. But while the GH3 is the work camera, the next one I buy will be the fun camera, so perhaps logic shouldn't carry the day. That said, GAS clouds the mind of even the strongest individual