Thanks for your kind words, Davis.
K2 is powerful content extension for Joomla, it’s non-commercial component (some of its module/plugin you need to pay to use).
Some other also have the same concern with you but in my opinion there is really no right answer for this question because it depends on what features you need for your site.
We and some other brands use K2 over other content extension because of useful features it brings out such as: Import/export, built-in commenting system, resizeable images, tags, social sharing, extra fields, … and for each JA template K2 is used, we provide additional style for K2 item / category pages along with default style of K2.
You can give it a try and make comparison and for SobiPro, I’ve never used it but will pass to template team for further consideration
Regards