[throwaway4aday]

Anything that will get your heartrate into zone 2 and keep it there for the duration of the exercise. It really depends on what you prefer to do since being consistent with it is the most important thing. If you're unsure, you could always join a gym with a decent selection of equipment and try each of the machines for a week and see which one you feel like sticking with. If you don't want to go to a gym then your options are more limited, pretty much just the ones you listed.

If you don't really do any exercise at all at the moment I'd recommend starting with just walking for 45 minutes, you'll need to do that or some other low intensity exercise for a while to build up to being able to doing 45 minutes of fairly intense cardio. Do a search on YouTube for "how to start running" and you'll find a lot of good plans that you can use and they generalize pretty well to other types of cardio.