all of them! I do a different cardio workout every session. Keep your body guessing. Don't let yourself get used to one. You expend more calories that way.
There really is not a BEST cardio to do.. I mean as long as it gets your heart rate up and burns calories personal preference is really up to you. I have a stiationery bike so I do that... if I owned a treadmill I would do that instead it doesnt really matter to me...
Bro cardio sucks in my opinion no matter how much you change it up or what music you listen to so you just gotta suck it up like the rest of us.
If you have access to a Pool, Swimming.
Otherwise, the best is to do something different each workout.
Some machines will work the legs primarily, others, the entire body.
Swimming works it all so that's why I like it best.