It would be best to actually drive it. That gets the transmission and axles up to operating temp, helps keep seals from drying out, and keeps bearings lubricated. Engines aren't designed to idle excessively. It would actually be better to keep it parked and use a battery maintainer than to just idle it for 5 or 10 minutes every week or so. Check your tire pressure too. Temperature changes can make tires lose several PSI.
Definitely true on the tires' PSI. My tires dropped hard during that frigid spell back in February. Also, it's not healthy for a car just to have "city miles." You need to drive it a highway speeds once in a while, for a decent amount of time, to prevent buildup of stuff (or that is what I learned growing up).