hmmmm well that's hard let me say what I like about both
Negril long beach to walk and enjoy, endless food option, it's familiar (when I want action I go here)
Portland speaks to my soul, makes me slow down and just enjoy. Drop dead beautiful scenery, genuine people, zero hassle.
If you can stretch your time to 10 days I think you can split, but with 7 you will be too rush.