For me, I think that it's a combination of all of these things, and none of them. If that makes any sense at all.
The best looking and sounding bass TO ME is a Fender Precision, black pickguard on olympic white with a maple fretboard - hence my choice of bass. But I don't know whether I'd consider it to be cool, in fact I look pretty nerdy when I play it but that is probably everything else... the wide leather strap, the bass height, and the fact that I am a nerd My super small and lightweight rig doesn't really add to the cool factor either.