IMHO the Sigma 19/2.8 seems pretty sharp on the E-M1.
I like it, but I am not a professional reviewer!
Manual focusing seems superb, very smooth and precise.
In M or S-AF MF mode magnification and/or focus peaking is active as long as one turns the focus ring.
As soon as one stops turning the focus ring the camera goes back to full view.
That's not what I want.
I have an Leica M to NEX adapter designed by Paul Habsch from Phigmenttech.
It also switches on magnification and focus peaking as soon as one turns the focus ring.
However, it only goes back to full view when halfway pressing the shutter.
The advantage is that one has all the time one needs to fine tune focus|