I've stayed at both and both are good. On balance I'd say I prefer the Divi, mainly because it is in the downttown area and within an easy walking distance to many different restaurants, etc. Buddy's probably has the slightly better shore dive, mainly because it's really two different dives depending if you go north or south. You can't really go north from the Divi because you'd be getting into the restricted port area. Downside to Buddy is that it's very popular with dive club trips and big groups that want to book up the boat trips as soon as they're posted. If you're planning to rent a truck and do mostly shore diving, I'd probably opt for Buddy's. If you're planning to do a boat-dive package and are travelling as a couple or small buddy group, I'd pick Divi.
Incidentally, I'd rate the restaurants at both places (Chibi Chibi and Lion's Den) as among the better on the island. I'd guess the two resorts are about 2 to 3 miles apart.