DJDB2, IMHO NEGRIL no question. Especially for first timers to paradise. Negril will give you what most expect. Lovely sand beach, awesome sunsets, cliff diving, tons of food and accommodation choices.
I agree do not rent a car.
You will see enough of MoBay when you land. LOL.
There is a 'cheap' way to travel which is JUTA bus. IRIE.
I have been to Jamaica several times (to every part) and I agree - Negril is the most beautiful. And, you can always find a local who will take you on a guided tour - by boat, bus or taxi to any other place you want to go. Also, if you choose an all-inclusive (worth it if you can afford it on the first visit), a lot of activities are included and you can just watch the schedule, go with a group and enjoy. As far as all-inclusives go - Superclubs are the best in my opinion. One Love!