I bought the GF 20-35 a few weeks ago and I am very satisfied.
The sharpness is formidable from edge to edge, the construction rock solid, the balance excellent.
At the same time I also used the GF 23: the performance of the two lenses are similar but the zoom is much more versatile.
In my PHOTO gallery you can see some shots taken with the GF 20-35.
The only flaw is the very high price but still well below, for example, the Hasselblad prices.