I initially liked the Aluminum but didn't like how sparkly it appeared under the lights in the hands on videos done during the Google launch event. While I generally like the Anodized Aluminum look, I just decided I didn't care for it on my phone. I also noticed the plastic piece at the bottom of the phone didn't seem to be a perfect match for the metal portions, it was close but in some lighting you could see a clear difference in color.
Because of this, I thought the Frost looked better than the Aluminum. The color still seemed to "pop" without the sparkles and I liked how the silver on the edges provided a nice contrast to the white. The bottom plastic piece also seems to blend in better in most light situations that I could see -- I'll be interested to see how it looks in person.
After watching the review videos, I'm still happy with my choice of Frost. Though I would have a tougher time choosing between the Aluminum and Graphite; I think Graphite may be my second choice, particularly with the way the Graphite color "changes" depending on the lighting. Just to be clear, though, I really like the look of all the colors; I think it is a great looking phone.