Everyone has valid points.

If you can find one small enough, I think a CX bike would be a great choice. More relaxed, comfy for commuting and errands, but slap on some skinny tires and it's basically a road bike.

I have a Bianchi Axis that I use for that purpose and I love, love, love it. I also love my lighter and more aggressive road bike, but for riding in traffic. with a backpack, etc, the CX bike is definitaly a winner. Plus cx tires/canti brakes are nice in sloppy weather. It is super, super comfortable. I'm not especially small though, at 5'6", and so it wasn't too difficult to find a good fit.