Over or Underexposure?

Personally what I would do is isolate the buildings from the sky, brighten and up the contrast on the buildings a little. Too much and it'll look weird. Then inverse the selection and reduce the exposure on the sky just enough to bring back a little more texture in the clouds. Happens to me a lot, the sky is too bright and I lose contrast / detail in the darker areas.

Love the photo though.

Well, perhaps one could argue the photo is a bit flat, so maybe bring some brightness into it. To me, overall it looks a little underexposed, so you could increase the exposure just a little bit, make the picture a bit brighter and try submitting again.

It's to small to really have a good look at it, but I would guess the buildings in the bottom (particularly the left side) might be under a bit. It does seem quite dark. But, again, this is a tiny little thumbnail, so it's hard to tell.