Yeah, not sure whether the Sigma will have more distortion than the Sony or not.
The Sony is not very compact. That's the main advantage of the Sigma. The 10mm loss at the long end doesn't matter too too much I think as one can crop.
Although the aperture closes very fast, the ability to have f2.8 at 20mm can be useful, for instance for indoor shots or when there isn't much light outdoor (dark forests, etc.).
