Well, I usually create partners for my sims myself, but if I didn't then it would depend on the compatibility between the two sims in question and the story I was trying to tell. One of my sims is an evil vampire, but he has a soft spot for his jealous human girlfriend and they are one of my favourite couples. Unflirty is a challenge, but with a bit of work they can also become affectionate partners. The only trait I think I would always avoid is Hates Children because I find it so distasteful. I'm not terribly fond of slob, glutton, noncommittal, kleptomaniac, mean or lazy either, unless again it suits the story. Of course there's also the idea that the 'power of love' can change sims for the better, in which case I will reset their traits or swap an undesirable trait with the re-traiting potion reward. Sometimes I will even make a sim with this in mind for a story. For example, I had a homeless self-assured lazy slob sim who manipulated his way into sponging off of a gloomy good squeamish sim. The good sim was such a sweetheart to him though that he fell in love and changed his ways, even going into charity work.
