Check, www.mozdivers.com this is a verry good organisation!
I been to Mozambique and Tofo 2 times in the last year the first time whe organised everthing ourselve and drive whit a car from JHB to Tofo etc.
There i meet the owner of Mozdivers and saw how they work i went back 8 months later with a group of 8 divers everthing organised by them and it was perfect!
You can do it yoursels also but believe me it is not cheaper! so it depends what you like the most.
Whalesharks are not so big between 4 and 7m i have seen really allot of them i was there the first time in March and the second time in November after 2 days of seeing whalesharks on the surface when we where going and coming back from the divespot whe where not intrested enymore! how menny times can you jump in? it sound strange but if you see every 5 min a whaleshark (or less!) and you have jumped around 20 times in the water and sometimes they leave instantly but other times they stayed around for so long whe where intrested!
1 of the last days whe where going to the divespot and whe seen 12 whalesharks togheter! OK then i jumped in again :-) that was imazing like a feeding frenzy there was realy a cloud of Plankton and the vis was only about 10 to 15 m and under water swim from 1 to the other! i have shot's whit 3 whalesharks togheter in a vis that is not more then 15m!!!!
So the whalesharks are cool but believe me the Manta's in Tofo are Imazing, they are all about 5 a 6 m! and on the cleening stations you so menny togheter!
If you need more information just ask! you can see on my website some videoclips from my first visit there.