Don't get hung up on which fitness class, machine or type of exercise is the most effective or is a better, more complete workout than the others. Most of us are not training for a major competition in a specific sport so those distinctions are not that important.
Do whatever you can, whenever you can. Choose some activity that you enjoy enough to actually do and you will be just that much further along the path to better health.
And remember this: Light or moderate exercise will improve your health and fitness. You can walk, run, do body weight squats and push ups, etc., for less than 30 minutes and realize nice health gains. There is no need to go long and hard, unless you feel up to it and enjoy that. Any type of physical activity is good for you!