Had you asked me when I was a child which I preferred, heroes or villains, my answer would definitely have been in favor of the latter. From Dr. Claw to The Phantom Blot, Captain Hook (the Dustin Hoffman version), Bowser, Ganon and a wide assortment of Disney-villains, the bad guys in stories almost always seemed cooler, more interesting and more charismatic than their goody-goody counterparts.
These days, however, things are a bit different. Yes, I do still think that there's nothing like a truly great villain and there have been instances when I decided to check out some work of fiction, solely on the basis that the villain seemed interesting. I would most likely never have watched Star vs. the Forces of Evil if it wasn't for Toffee, to name one example.
That said, I can also come up with plenty of stories in which the hero is an engaging, complex character and the villain is simply just there because the story needed a villain. Take Casablanca for example; one of the greatest movies of all time, to be sure and yet, does anyone actually think Major Strasser is more interesting than Rick Blaine?
While we're at it, I must confess that as I grow older I like the concept of the endlessly recurring arch-villain less and less. Olrik from the Blake & Mortimer comics is a particularly flagrant example of this kind of character. Now, I haven't bought any new Blake & Mortimer in years, but out of the albums I own, there are only two in which Olrik is not present in some capacity. There are twenty-two Blake & Mortimer albums on my shelf. That means that twenty of those feature the same villain. To be fair, some of these albums tells a continuing story over two or three installments, but that's still a lot.
Don't get me wrong, I'm not saying that every villain should perish at the end of their first appearance. If you've managed to create a good villain, than I can certainly understand wanting to bring them back for a re-match or two in order to further flesh out their character. However, after awhile it starts to become forced and trite. Plus, it risks hurting the villain's credibility: After all, he didn't manage to kill the hero and take over the world the other umpteenth times they fought, so why should this time be any different?
Ultimately, I prefer to judge a character based on how interesting they are as a character, regardless of what role they have in the story. If the villain's the most compelling character, than that's great and if that honor goes to the hero...well, that's great too.