"Beauty is in the eye of the beholder".... I think most of the non-angling population would find it a struggle to find anything about a fish beautiful... Koi being the exception maybe?
However, personally I agree about the perch, striped up to the max (so out of a nice clear river or pit, not some translucent thing thats come out of a cloudy pond). A well-marked crucian is always nice, all gold and orange... likewise a big rudd in its prime.
However, the "best looking" fish I've ever caught was an extremely dark and scaly mirror carp out of a gin-clear pit. Only mid-double, but absolutely perfectly formed, almost black on top and giving way to a scrambled-egg yellow belly. I'm pretty sure any non-angler would think it profoundly ugly, but I was over the moon!
On the original subject, I think barbel are stunning!! Not sure how I'd feel if not spent soem time pursuing them though....