With big fish- you can't go past the Whale Shark. There are many different locations around the Maldives for whale sharks- the most famous is of course Maamigili region at the bottom of South Ari Atoll, but as you have stayed at Sun Island you will know that already. We see whalesharks in the N Ari as well but definitely not as regularly as in the south.
Another decent island with a very good dive center for experienced divers is DIVA (formerly White Sands) which is close to Maamigili. Room prices are reasonable from what I hear but consider Nov to be already high season so rooms are more expensive. (I worked here for a short time before moving for another job opportunity) The manager is very experienced in this area and approachable. At the same time IMO this is not so good for the beginner divers as a lot of responsibility rests on your shoulders diving with this outfit. The groups can be large (well larger than 4/ guide, which many resorts practice) and the dive sites in the Digurah Kandu are fairly deep (15-20m to the top of the reef) and they are all exposed to current which at times is incredibly strong (stronger than you can crawl against). Descents must be co-ordinated with no fluffing about at the surface but the diving can be spectacular with colour and fish. Divers must be prepared to take control of their own dive with no hand-holding from the DM. Nitrox is recommended for divers with good breathing control.
For those less experienced, diving the outside reefs is usually easy but can be really rewarding though with whale sharks in the shallows, as well as the usual suspects (Whitetip reef sharks, rays, turtles) For the keen eye there are leaf fish, ghost pipefish, scorpion and stonefish. The current gets stronger at the corners but there are good chances to see mantas and schooling mobula rays here as well as Grey Reef sharks in the deeper areas. Just take care not to get pushed out in to the blue.
The outside reef around Maamigili is definitely not as colourful as the inside reefs as they get a proper pounding from ocean swells but the big boys congregate here in numbers. The big problem with Maamigil is the boat traffic. I stress when I'm there as there can be a dozen dhonis (local boats) doing figure 8's arounda whale shark with 40 people snorkeling with a shark. Common sense is not that common here.
In November you have more chance to see whale sharks around Bodu Finolhu Thila which is just a half hour east of Sun island or around 50 mins from Diva. The reef is fairly boring and it is a bit hit or miss- sometimes 50+ mobula, eagle rays, whale sharks but sometimes it's a no show. The thila itself is deep (top at 24m). Resting on the bottom are plenty of whitetips and if your guide is good
he can show you the Halimaeda Ghost pipefish in one of the small overhangs at 27m. They are freakin small (maybe 4cm).
Mantas are fairly seasonal but every so often you get lucky out of season. Maybe a week back we had approx 20 on the west side of North Ari. According to local lore- they shouldn't be here at this time of year. However we are also experiencing unusually calm seas, warm temps (29 degrees) and lots of sunshine. We had a small baby manta in the lagoon yesterday (maybe 1m across) and another larger juvenile at the far side of the lagoon where we do DSDs and orientation dives.
Regarding the scubaboard policy about divulging workplace info- I have no idea but you can PM me.