I personally would, and did, choose the zero-turn option mainly because you will more likely be able to mow your yard if you are sick or injured. There are times when you feel like pooh but can still sit on a mower for an hour or two but the thought of walking behind, even a self-propelled, mower would be a nightmare.
And then there's injury, a twisted knee, a sprained ankle, etc.. I personally broke my kneecap in half in a head-on collision 2 years ago and am oh so thankful that I could swing my full leg brace onto the mower and get 'er done.
That's just me of course. I'm 58 year old now and as you can tell, relish riding. Then, if I'm healthy, I have time to exercise.
Good luck in your decision, I'm sure you will make the right choice for you and your particular lifestyle. Let us know what you get.