My choice of the two would be the Radisson. Right in the middle of the Palm Beach area. Can walk to numerous restaurants and bars. Very nice hotel and grounds are really nice. Somewhat less crowded than the Marriott in my opinion and I think the beach is nicer. Car rentals are not a problem and relatively cheap in Oct/Nov. You can decide if you want to rent when you get there. I am in same age group and I love to take rental car or jeep and explore the entire island. You did not mention how long you were staying or other interests. Can give more info on things to see if you like.