Hey Mark,
Can recommend using Dive Sportif. We went with them in June this year for two weeks and stayed at the Hilton Tobago - primarily because it had its own on-site dive centre, World of Watersports, and they do Nitrox.
Diving was top notch, especially if you like drift diving!
Only one wreck, the MV Maverick. A former RoRo ferry that used to ply between Trinidad and Tobago, she was deliberately put down for divers in 1997 and lies in 34m to the sand, and is completely accessible for penetration.
Any way, hope this helps and check out the URLs below for more info:
<a href="http://www.sportif-uk.com" >http://www.sportif-uk.com</a>
<a href="http://www.worldofwatersports.com/wow/" >http://www.worldofwatersports.com/wow/</a>
<a href="http://www.adventureecodivers.com/AEDWreck.html" >http://www.adventureecodivers.com/AEDWreck.html</a>
<a href="http://www.tobagodiveexperience.com/NuSites.shtml" >http://www.tobagodiveexperience.com/NuSites.shtml</a>
Cheers and dive safe.
Bren.