I have owned the m.Z 9-18 longer than my first m43 body. I think the old 4/3 9-18 was slightly better corrected, but the m43 version is wonderfully compact.
Bought the 8-25 for it's extended range, so much more flexible than 9-18, but definitely chunkier. If I want wide I pick up that one first. The little zoom still comes in handy if I just want a wider option that I can stick in a pocket 'just in case'
I know when the PL 7-14 came out, there was a lot of talk about purple blobs if used on an Olympus body, but could be corrected by adding a yellow filter at the back of the lens. Does this still affect OMS bodies?
The old 4/3 7-14 was extremely well corrected optically (straight lines at 7mm!) while the m43 version is corrected in software.
Of course, if you want really wide, there are several inexpensive MF fisheye lenses.