Either is fine. But the wider tire will make a big difference in any loose gravel, mud, or sand. I would suggest go with the one with wider tire, and if you end up doing a lot of miles, and want to go in that direction, then you will have refined your interest and could switch at that point. For now, for around the neighborhood and parks, I suggest the wider tire.
Regarding speed: if you are interested in fun and fitness, speed is not really relevant. Being at one level of exertion for an hour will get you fit whether you do this with a heavier bike for 9 miles or a lighter bike for 12 miles.