The Great White is the largest and has a high percentage of fatal attacks. The Bull shark is responsible for a lot of attacks on swimmers and people in shallow water. From reports it seems a lot of these attacks were only one bite but a large percentage of the victims died of blood loss and shock. It is likely to be the worlds number one killer shark on swimmers. I have heard of a lot of encounters with scuba divers but have so far been unable to find any attacks.
The Oceanic Whitetip usually moves in groups or schools and can be extremely savage. It is thought to be responsible for a large number of fatal attacks on shipwreck and air crash victims. This shark very rarely comes near shore and prefers the deep ocean areas. I have heard of one fatal attack on a scuba diver in the past and a lot of close calls.
The Tiger shark usually spends daylight hours in deep water and comes into shallow areas around reefs and coastline during the night. It has been responsible for a large number of deaths. This includes swimmers, surfers and scuba divers. Many divers swim with these sharks with no problem but a large Tiger shark is more than capable of killing a human.
Overall, there are very few fatal attacks on scuba divers. I have not been able to find any over the last twenty years except for one in 1991 and two in 1993. Ironically these were both in the same month. They were all by Great White sharks.