If you marry someone, which house do they go to if you have multiple houses owned? I want to marry Mjoll but the last house I bought was in Markarth to become thane, but I hate Markarth and wouldn't want to live there at all. I'm hoping Mjoll moves into Riften or Solitude but I can't be sure until I've married.

Is there a way to determine or is based on the last house you bought?

After getting married, you can enter a dialogue box with your wife, and choose which of your houses you wish to live in. Post that, if you want to move her, just talk to her again and tell her you're moving (there are options to do that).

Oh sweet! Thanks, was afraid I would be forever stuck in the city of stone and corrupt guards and cannibals.