Upload & Sell: On
Zephoto, there aren't many choices for WA on a NEX. Basically, 2 native WA lenses, the Sony 10-18mm zoom. I thought it was good, and no more, but Andrew (snowboarder), has found it good enough to buy it, which is serious praise coming from a serious guy. The other one is the Touit 12mm. I liked it enough to buy it, and haven't looked back since.
As far as Leica goes, there is "only" the WATE (wide angle tri Elmar) 16-18-21mm. It has absolutely no corner issues or colour shift even with the NEX 7 (!), but it cost a fortune, and I thought the IQ was a bit less inspiring than the SEM 18, itself not as brilliant as the SEM 21 and Elmar 24.
Voigtländer make 2 lenses which you could use, a 12mm and a 15mm. I don't remember anyone regularly posting pics wth the 12mm, which says something. There are quite a few pictures with the 15mm coming from good photographers, but they require CornerFix, and, even then, are not really clean in the corners IMHO.
As far as finding info related to what I have written, a lot of it is based on NEX 5N, which is the same as the 6 IQ-and-lens-compatibility-wise.
Biljtje, you are not alone in having such as high opinion of the Sigma twins. Bobu (Boris) thinks the same, and I trust his judgement. He actually says that the lens in the DP2M is a bit better than the one for NEX, and is every bit as good as the Summilux he had at the time.