Well, he is a bit of a doofus, but he's not a moron like she seems to think. There was one argument between the two of them not too long ago where he protested that he was smart because to be a Templar you had to have a pretty extensive education. It's essentially the same as the sisters for the Chantry go through. I think that's a pretty fair assessment. I do love the antics between the two of them though. I'm not generally a big fan of conflict, but the conflict between them is pretty funny. Oh and once you develop a relationship with Alistair, and you talk to Morrigain, her responses are pretty funny. She makes a comment about how she doesn't get what I see in him because he's such an idiot. One of the options is to reply, "He may be an idiot, but he's my idiot." I picked that one. It gave me a good chuckle.
Yeah Morrigan's and Alistair's interactions have to be about my favorite so far. The two personalities just bounce off of each other so well it's entertaining to watch. Admittedly Alistair is growing on me the more time I spend around him. I'm not sure if that's due to anything he's doing, or if it's simply the fact the only other male romance option recently tried to kill me.
Though I'll have to romance him and talk to Morrigan now. That sounds like fun.
As a woman you can romance Leliana too.