Columbia is a perfect location to split the difference for commuting. 200 is a toll road but should make for a pretty smooth commute to Rockville. Baltimore commute times will vary based on location of destination, but you have some options of I95 to downtown or going 29/70 cutting through the west side. When commuting to Hampden area of Baltimore going 29/70 was very predictable and about 35/40 minutes each way.