Definately Digicel, I have LIME Iphone and Samsung Galaxy Tab with DIGICEL 4G. So far i have run test from Kingston to Portmore and Spanish Town.
LIME best speeds are between 1-4Mbps
Digicel best speeds are between 3-13Mbps
Digicel did their home work.
Check out my Iphone page on facebook.
or my iphone web site, http://iphone-charger.net , for great information and the best deals on Amazon,