Most Helpful Guy
It's not that simple or straightforward. I have seen couples with similar personalities, as well as those who are completely opposite.
Both are possible. We usually attract people who find at least SOME common ground with us, even if their personality is totally opposite.
Most Helpful Girl
In my humble opinion I think that while opposites can attract, the level of intelligence, the intellectual ability of the 2 people is most important. We don't think about this at a conscious level most of the time but a long-lasting relationship has to have equals or near equals and intelligence. Otherwise one partner loses respect to the other. So I am answering your question by using a tangent for an answer, both opposites attract and similars attract but it is the level of intelligence that keeps the relationship going