Hi jajambo, I was in Sipadan in Feb, just before going to Maratua. I should tell you that Sipadan/Mabul was far better than Maratua/Sangalaki/Kakaban. There are similarities, but Sipadan has better sharks and other large creatures and Mabul has better macro life than Maratua/Sangalaki/Kakaban. I don't know about Derawan because I stayed on Maratua and Derawan was too far to go to. I'm not telling you not to go, but just that it was not as good in my opinion.
Of course, Sangalaki has mantas, but we did not see any during two trips. But there are many large turtles on Maratua. Plus a school of barracuda (again, Sipadan is better!). And the jellyfish lake on Kakaban is fantastic. I would not recommend Maratua Paradise Resort. They are overpriced for what they offer and management does not seem to want to keep their guests happy.
Sorry I can't help much more, but if you find what you are looking for, I think you'll have a good time...