I like either Markarth or Windhelm right now, although it changes often.
I like the decaying, run down, snowbound look of Windhelm. I dislike Jarl Ulfric, but Windhelm is nice, (excluding the Grey Quarter), even it is not in great condition. It's just so ancient and imposing, and the castle is literally right there, above the whole city. I also like the thin, confusing passages. It also doesn't hurt that it's the nicest house (in my opinion). The racism/stormcloak influence bugs me though.
Ever since I woke up in Markarth's temple, it's been one of my favorites. The high, craggy spires and the mountains surrounding the city. The reach in itself is really beautiful, I love the waterfalls and all that. My favorite used to be Riften, but it got old really fast. Also I don't like how un-defensible it is. Markarth and Windhelm could easily be defended against a siege. Easier, atleast.
EDIT : Actually I also really like Falkreath. The whole forest setting reminds me a bit of Chorrol, except damp and wet and without walls. I like the wilderness theme, the only thing I don't like is how you can't get a home without Hearthfire.