You probably noticed the trend of making custom designed plugin/theme options UIs, especially in the commercial ones (on CodeCanyon for example - custom boxes, tabs, accordions etc).
I personally believe that UI should be unified in the first place and that is really easy in WP to achieve using some core's default HTML structure + CSS classes => following the styling guide.
However it is maybe sometimes not enough and that's why why there is that trend. Another reason could be "branding" or just some "coolness effect".
What do you think about this? Do you prefer some custom designed UIs or the default one and why?
P.S. The main reason I ask this is also because these days I started with plugin development and I trying to make this decision of which path to choose.