I stayed at the Manta Lodge in Speyside, the rooms were pretty good and they also have a decent restaurant attached that does a good breakfast (included in the price) and dinner. All in all it was a good choice at what I think was a very reasonable price of about 100 USD per night for a double room with balcony and sea view. There are about three or four restaurants within easy walking distance of the hotel, but to be honest the best food we had in Speyside was at the hotel.
I also did my diving with them and got a very good all inclusive price for the accommodation plus five two-tank boat dives.
The diving in the Speyside is excellent with a wide variety of sites including, walls, reefs, and the amazing pinnacles. Only downside was that the vis was not great when I was there in September due to it being the rainy season, March should be much better. Even so I saw Manta's, Eagle, Electric, and Sting rays, as well as nurse sharks, and of course all the smaller stuff.
Just remember the currents can be pretty strong in Tobago, so be prepared for some energetic dives!