Olympus mZD 75 f1.8
One of the sharpest lenses I have ever used. The problem is, it's equivalent to a 150mm in 35mm terms. It's not often you need a lens of that focal length. Having said that I enjoy using this lens wide open. I am, by nature, a long lens type of guy. Many others like the wider view of things but my main lenses tend to be in the 50mm to 135mm range. And that's using them on full frame and APS-C cameras.