I've seen Mantas a couple of times. Once there was just one in December.
Another time I snorkelled with a load in early January. They move with the
season. I believe they're more likely on the west side of the atolls from
January onwards and then the east side from about July onwards.

Never seen a whale shark.

But for me the best sight you see in the Maldives is the thousands of fish
you see on every dive. There's schools of fish all over the place. You
take a picture of a big fish and when you get it home, you realise there
about about 40 other ones in the frame.

I've been from December until April. Don't go in the first 2 weeks of
December. It rains a lot and it can rain all day. Around about the 15th it
stops raining. Then it's generally dry until about April. In April it
starts to get very humid. It's always humid, but in April it's noticeably
worse. In about May, the rains start again.

It's easier to spot the rainy months. They're the cheaper ones.

Jason