Best wide angle lens?

Hello

I have just bought a nex-5N and am looking for the best quality wide angle for architectur (e and landscape (within reasonable cost)

I will be using the lens between f5.6 and f11 mostly

I was choosing between:
15mm voigtlander
21mm voigtlander
19mm sigma

Sharpness is important as I can not recover detail in pp
However distortion is not such an issue as I can correct

What do you guys think?
Any other choices?

Thanks in advance

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http://www.haroldmiller.me