Anything that you'll actually do every week and gets your heart rate up. Bonus points if it gets you outside. Walking. Running. Bicycling.
Personally, I like biking to work. Integrates the exercise right into my routine and doesn't really take that much more time than my other commute options. I also do longer weekend rides (40-70 miles).
Personally, I like biking to work. Integrates the exercise right into my routine and doesn't really take that much more time than my other commute options. I also do longer weekend rides (40-70 miles).