If your new to exercising, I would definitely recommend biking. It's fun, burns a bunch of calories (depending on your speed and how long you bike for, obviously), and it's low-impact. Great for your heart, great for your legs. The most important thing is that you do something that you really enjoy, otherwise it'll be a chore, and it'll be much more difficult to make progress.
I would love to ride my bike every day, but look at my last post. :(
