Edit: In all seriousness, It really depends on how in depth the skin needing coded is. I mean coding is coding and doing it for other software is almost a copy & paste. XF has a powerful style property system that can do things without even touching a template. With vB I always find myself in the templates or adding things to the additional.css template.
Your going to get 1 answer here I think and rightfully so.
Some other changes like layout changes require getting into the CSS code for which there is a style properties interface. You can also edit the CSS and HTML templates directly, but of course that requires coding ability: