> So you would do the Sigma 8-16 over the Sigma 10-20?
For sharpness and image quality, definitely yes. The only UWA that are better are the Nikkor 14-24/f2.8 (talk about a brick!) and a couple of the Zeiss offerings, all of which are in the vicinity of 3x the price. Search our 3rd party lens forum for some samples - they are really good. The 8-16 has fairly good distortion control for a UWA, but you'll still need (not want) to correct it in post processing. The Sigma 12-24 FX Mk I is the best controlled UWA and I *absolutely* always correct distortion even on that one. If you're shooting architecture or something with straight lines, there are NO UWAs which do not demand distortion correction in post.
For completeness, both the 24-120/f4 and the 18-105VR also have fairly significant barrel and/or pincushion distortion, depending on focal length.
> I could do some crazy portrait work with the kids at 8mm...could be fun.
LOL... I have occasionally done this with my faithful dog. He doesn't complain when his portraits exaggerate his nose! (I even did it with an 8mm circular fishsye! He's so patient with me...)
Sorry about changing around on you... some of your requirements are in conflict: maximum/ultimate IQ and minimal size.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!