Here's a link to an article about the origins of butterfly koi, if interested: http://www.koistuff.net/butterflykoi.html
When I first got into the koi hobby about 4 years ago, I was attracted to the solid colored butterflies (black or platinum) b/c they reminded me of images of the mythical pheonix bird when they swam. After keeping koi for awhile, I began to feel that they distracted from my true koi and were not pleasing to me anymore. I kept a black butterfly that is currently about 16" for sentimental reasons. You don't really notice her in the pond until feeding time.
All strains of koi have been manipulated by humans to produce various qualities deemed desirable by individual breeders geared towards groups of hobbyists. I would be going out on a limb to say that many people early in their koi-keeping careers may be attracted to butterflies but change later on after learning more about the hobby. Of course, that would be strictly conjecture.....
It seems to be a matter of personal taste and where your focus is in the hobby. Personally prefer "normal" koi, but as Dick stated, can see an elegance to some of the varieties of "dragon koi."