The best exercise is something you enjoy doing. Try a variety of activities. Running, cycling, elliptical, swimming, hiking...for cardio. Then add some resistance training. You can take a variety of classes if you like to be in a group or you can do these on your own. The key is doing something you enjoy, otherwise you will find excuses not to exercise.
I agree about doing something you enjoy! If you hate your exercise, you won't want to keep doing it. It also depends on what your goals are. What I want to get slimmer and into my best shape, I like to go running because I get the quickest results with running. I also do strength training with whatever cardio I choose to do. I currently have to do low impact exercise due to medical reasons, so I use the elliptical machine. To avoid getting bored at the gym, I listen to music or watch the personal TV's.