I love Mayfield for the sheer beauty of the nature and immersing myself in that--plus dips in the river. But that said, to get the most out of your day excursion I think a combined trip of YS and Pelican bar would be ideal and give you a nice taste of some of JA outside of Negril--you could also fit a black river safari into that. It would make for a comfortable day trip--no need to stay somewhere overnight--in fact you would be back in time for dinner in negril.
Here are some sample tours from Rocky's taxi website http://www.rockystaxiandtourservice....excursions.htm
I think that Alfreds, Clives and Juta also have day trips listed w/prices.