Look at your route and the road/path conditions. If the route is all dirt and alley and potholes and ditches then lean toward the MTB. If the route is smooth pavement then lean toward the roadbike. If the route is mostly pavement with a few railroad or trolley tracks and a bunch of manhole covers and sewer grates to negotiate along with assorted city road debris then look at a bike with probably 700x35c tires with a road orientation but a more upright riding position. That amount of money should put you onto a fairly decent commuter bike with enough extra for fenders and a rack.

Just my opinions, adjust to fit your personal likes and needs.