Speyside has the best diving on the island.  however, the problem with
Tobago is that it is close to Venezula and the viz can be quite bad
depending on which way the Oronoco Flow is flowing.  Rich nutrients
bring in all the abundant fish life, but, the viz can really get bad.
I have been there a couple of times.  16 months ago I was in Speyside,
viz was poor and the current ripping.  Also ran into a heavy down
current. Time before that it was calm, viz was good and no currents up,
down or sideways. So, check with your operator, some months it is
better to dive the northside of the island (try around the 2 sisters
islands)