The panasonic cameras all lack tools for still photography, which the olys have.
For example, we need a user setting for limiting the slowest shutter speed, in A mode, with the flash enabled.
The panasonic defaults to 1/60. So you will get motion blurred subjects far too often, in A mode, with pana cameras.
The olys let you set the speed, to 1/100 or 1/125, so the shutter speed can range from there, up to the sync speed of 1/250 (which is also better than the panasonic, I believe).
The olys allow you to set auto ISO, in M exposure mode, which means you can have full control of DOF and motion blur, while still trusting the metering.
Panasonic does not allow this. So A mode is unusable. S mode and P mode are out all the time, when using a flash, so that means using M mode only, all the time, with panasonic cameras.
Oly's have much nicer colors and jpgs, out of camera. With Pansonic, you are pretty much forced to shoot raw, all the time.
The em5 has the built in view finder, which the nauticam housing beautifully supports...
After trying just about every decent camera released in the last year, I just bought the em5, and am loving it!
Just about ready to order a housing.
HTH,
Don