Your traveling will be easier when you have enough time in to use the zed's, that takes six months on AA. It's nice to know that you have options in case you get stuck. As to cities easy to visit, something also to consider is that unless you want to hang out at the airport, most cities will also require a car. ORD is easy and no car is needed as is NY and even MSY. I have also done a day trip to Mall of America they have or had a shuttle that took you to and from the Mall for next to nothing. YYZ is not a bad choice but public transportation from the airport is not great.