I would say both.
But wait, you cry, does that make your soul-mate lacking??!!???
No, and I'll explain.
Everyone's different. There's music my wife likes that I generally don't see the appeal to. There's books I read that she doesn't care to tackle. There's certain sexual activities that one or both of us could care less for, both the other can't get enough of.
This doesn't make me love my wife less. In fact, the idea that it would be a problem to the relationship, because we have differences, or because we've developed different interests over time, is the reason many people jump into serial monogamy.
OMG, I found this chick that likes to play WoW, and my sweety doesn't. I must have made a terrible mistake!
I prefer to focus on the enduring love we have, and take those differences as being inevitable
, and they are usually trivial compared to our groovy long term love.
There's a guy, for instance, she had been smitten with not long ago who was a heavy duty rockabilly enthusiast. There's a guy who she's attracted to now that is way heavier into native American spirituality than I, which she digs. I know that they'd have a lot more to share on those topics that I would. Doesn't make me less important to her.
The one thing that we have that never is lacking is love and affection for each other, and that's a hole that doesn't need filling. It also doesn't mean that if she were to receive more love and affection that it makes what we have somehow less. I would hazard to venture that it would actually make it more.
Then there's the occasional business trip I might take, or project that consumes most of my time, or worst case my untimely death or serious illness. In those situations there's definitely gonna be a dent in the romantic love and affection department. Nobody could replace me, but it would be a good thing if romance didn't decrease to little or none.
So as far as romantic love and affection, I'm in the Complement camp in most cases.
But there are assuredly many supplementary bonuses to the poly lifestyle as well.