offcourse, the service is the most important.
but i think design is very important too.
what i think is that you obviously make a website to share somethings you want people to know or have.
so service has got to be ur first choice. It has got to be ur goal. but not the only one.
Design is also very imporant.
for instant, if you go to a website, it looks so cool that ...., you will try to learn how to work it and try to find where things are.
but if a website looks crappy, but it's easy to use, then people won't stay around and will just leave.

just like these "downloading softwares" or WEYCT(what ever you call them), if it has some cool shit in it, eventually, you will learn how to work w/it cuz you know ur work is not gun' be without prize.
if it looks cool, you might stay around a lil' longer even if it doesn't have cool shit in it.
if it looks crappy but eaZ to use, you will use it for couple of mins and then un-install it.
thats from personal experience.
hope my opinion helped you out.
good luck.