I'd have to say smarter or just about the same. Actually 'just about the same, but maybe slightly smarter' or more practical (they usually are) or more socially apt would be nice (I'm not calling myself a social retard, I just tend to approach social situations as mathematical problems I solve based on experience rather than... well, social situations)
I don't think I've ever met more than one or two potential partners who were significantly 'smarter' than me purely on a brain-power basis (i.e. IQ-wise) but I do know several that I've been academically or intellectually impressed with and those tend to be the ones I fall for. I'd actually say that I use relationships as a form of self-development.
For example, my last relationship really improved my work ethic as she was significantly more driven, cultured and (I'll admit it, mature) than I, and lived up to her (quite darn amazing) potential a lot more than I did. She's not necessarily smarter than I am, but I certainly was intimidated enough to have to up the ante on my end and live up to that. It's certainly made me a better person, and it's shown me that relationships are a fantastic means (for me, at least) to actually get me to make an effort. Heavens know I need that.
But yeah, I either need to be challenged when it comes to my strong suits or complemented when it comes to my weaker ones. If there's no potential for personal growth in a relationship, I can't imagine myself avoiding boredom past the initial stages of being in love. So either smarter or just as smart but better at other things would be my answer.