When choosing a partner, you need to look for someone who is compatible with you. Your prospective partner should have similar goals and desires in regards to finances, children, and other major parts of life. You should also seek someone who brings out the best in you and doesn't tear you down.
The most important thing to remember when choosing a partner is that the way a person is now is pretty much the way he is going to stay. People don't really change that much in the fundamentals. If a person is selfish, for example, you can't expect to be with that person and change him or her.
I think an ability to effectively communicate is essential. This other person is your partner and you each have to be able to talk and trust that the other person is really listening. If one person isn't talking for fear or annoyance that the other person isn't tuned in, then the relationship is going to struggle. WHAT you communicate about is also important. Each person has to feel validated in a conversation whether it is about where to go to dinner or whether to have a child. All of the little and big conversations deserve the respect and "give-and-take" of good communication.
I do think that some shared similarities are good in any relationship, but I also believe in the saying that "opposites attract." I would suggest that, in looking for a partner, to make sure that you both have similar goals in life (while they may differ on the specifics), that both of you share a certain level of intellect, and that you both are not petty.
A shared sense of humor really helps. Humor can help get people through rough times and can also help them bond even during good times. Shared values in general are important, especially assumptions about what's really important in life and what goals are worth striving for together.
About Post #2... Hmmm... that second part is asking a bit much!
I do definitely agree with the first part. You don't want someone who is way smarter or dumber than you. But I think that you also really need to pay attention to things like attitudes about religion or money. Those are things that can really ruin a relationship and so why start with someone if you're not compatible in those areas?
My opinion about this has changed greatly in the last two decades, but if I were giving this advice to my very own daughters I would tell them this:
1. find someone who is intellectually equal to you (or very close)
2. find someone who unconditionally adores you
I believe very strongly that love is more of a choice than a feeling. Both of the above have managed to be the two things I consistently fall back on and realize are the reasons my husband and I have maintained such a dynamic but ever deepening love relationship.