If you like hiking...you'll probably enjoy Mayfield Falls more. You can do both Mayfield & Pelican in one day...but you'll end up spending a lot of time on the road as they're quite a distance apart from each other. If you visit Mayfield only and leave around 9am...you can be comfortably back in Negril by mid afternoon.
YS Falls & Pelican are more commonly visited on the same day as they are located a short distance from each other....you'll be back by late afternoon or early evening from this excursion.
Have fun!