I'm using the e-m5 and an e-m1 for all my photography.
My uw setup is the e-m5, a 12-50 zoom and the panasonic 8mm fisheye. I originally bought the e-m5 specifically for uw as I didn't want to carry a full size housing and ports that my Nikon gear would require.
As it turns out, I ended up selling all my Nikon gear once I found out how good the m43 system performs. And I shoot professionally (photojournalist/portrait) for my career. It's that good. The only problem has been auto focus while on c-af, which I would say is not very good in the e-m5, but is almost the equal of the pro Nikon cameras in the e-m1.