I've been really liking the X3 lately, but admit that the X5 is generally better looking. The X3 front bumper and headlights looks meek in both regular and M sport iterations, and I agree that the swoop up of the lower edge of the rear windows cheapens the CUV. I think the dashboard could be a little nicer around the nav screen, and I wish I could get an F30 M sport steering wheel with an X3.
What I don't like about the X5 is the split rear hatch and I think X3 rear seat headroom is better than X5s. X5 3rd row seat is such a joke. I like the size and weight of the X3. The X5 uses the old generation gauge cluster.