This.A bit of both, but I learn towards functionality. If I'm gonna have to stare at it's back for hours, it might as well look decent enough. But mostly if I'm going to use it, I want it to be useful. As for catching, I usually only catch what I need as well.
Granted I think Crobat is one of the coolest looking pokemon I have, and Ampharos is ugly as sin... but meh, I use both.