Neuroticism: prefer low levels in myself and other.
As a personal matter, I strongly believe being over 50% neurotic can't do any good for a person. People are ok, lovable and great and all even to higher neurotic scores, but they'd be much better off with lower neuroticism scores.
Openness to experience: wide range is ok, apart from the extreme 5% either way.
Agreeableness: wide range is ok. I'd like low agreeableness to be balanced by being open or calm, as opposed to neurotic or "closed-minded". Imagine a crackpot or some closed-minded person sticking to his guns no matter what. Wouldn't want that.
Conscientiousness: I think it takes an effort to be conscientious, and optimum would be about 70% on the scale from 0 to 100. People with Low conscientiousness seem unreliable, non-accomplishing liars in the worst, and too conscientious people seem to lose the idea of why we live in the world in the first place, important part of which is to enjoy life. Still, I generally look up to the people who are more conscientious than I.
Extroversion: I'd prefer people to avoid being extremely introverted, or very extroverted. It's too freaking slow to get anything out of too introverted people, while much too extroverted people shut me down, which is a rare occasion.
As a follow-up question, are there some Big 5 attributes you'd dislike in a mate?
Some attributes - or levels in attributes - that would warrant a person to develop them for their own sake?