The new guidelines basically say that everyone should get 150 minutes per week of moderate intensity activity or 75 minutes per week of high intensity activity (this part has not changed) BUT the difference in the new guidelines is they do a better job of emphasizing that a little bit is better than none, and that it isn't just the planned exercise part that is important, but also important to generally not be sedentary. If you choose to do vigorous activity make sure to work up to it. The biggest risk of injury/health dangers with exercise is when people jump in and do too much too quickly.
If you are only going to do one kind of activity, make it weight bearing aerobic activity (i.e. walking/jogging, not swimming/cycling). Though of course it's better to incorporate aerobic, resistance, and flexibility exercises.
Edit: For context, I am an exercise physiologist who admittedly doesn't always meet these guidelines myself.