I have to add that muay thai is definitely my cardio exercise of choice to get me pumped up with yang, wherea swimming is great for yin, but having a good workout.
But on the real, for a more practical and easily accessible form of cardio (or rather one that does not require the consent of another partner), I prefer swimming. Best of all worlds right there.
It's too bad the water is ass cold right now, even in Miami.
Trail running > hiking for a cardio blast which is why I started doing it.
I no longer take group fitness classes as I was finding it stressful to make it to a class on time. Running I can do on MY time.
My mother in law does circuit training in the woods next to her house. This is an awesome idea. I have a half mile trail loop in my backyard will set up stations for variation in my exercise routine. I don't have to be concerned with someone stealing my equipment if I leave it.
Yoga can be a cardio work out in spurts. A class of power yoga nor bikram does not keep my heart rate elevated the entire time.
I do a full sprint for 45 seconds, then about a 60% exertion jog for 15 seconds, which makes one "rep." Usually do about 6 to 8 reps, but up to 12 to 15 if I'm really feeling it. Same effect as a conventional 45 minute cardio workout, with an added metabolic boost for up to 36 hours afterward.
sprint training... much better for you than distance running, both for your knees as well as rapidly increasing your VO2 max( maximum volume of oxygen you can absorb while exercising)