I use the road bike whenever possible. It's a pretty durable bike, a Windsor Fens from BD, and I've fitted lights and a rack. But it's way more fun to ride than the upright bike and less tiring too.

I do have a Giant Seek 0 for winter riding. I don't use it in the summer much. I take it maybe once every month or two just to keep the cobwebs on it down. It's probably 20 pounds heavier than the road bike, and upright, so the wind can be a killer on it. But in the winter when the wheels may slip sideways with no warning (even with studs, icy ruts and wet gooshy snow can surprise you), the upright posture lets me put a foot on the ground very fast, push myself back up and keep going.