Looking at the speed charts the fastest creatures in the sea are typically stated as either the swordfish or sailfish:
If these numbers are true then the billfish cannot be caught by any other predator based on speed alone. However, it might be that the speed of the Mako shark, usually regarded as the fastest shark, is actually understated, for example see the video here which at least puts the Mako faster than the Tuna (unlike the aforementioned speed charts) although it does not mention if it is faster than the billfish:
YouTube video titled: "Shark Week- Mako Shark's Speed"
If this video is factual, it means the Mako might be faster than the Orca and that a school of Mako sharks (weighing up to 450kgs) should be able to easily devour Orcas (4-6 tons) in piranha like fashion, also being able to escape by diving to depths where the Orcas cannot reach them. This contrasts with Great White sharks which are a bit slower and sometimes fall prey to Orcas, and I don't have a source showing Makos being eaten by Orcas.
So what do you think, what is the top predator in the ocean: is it a billfish such as the sailfish, the Mako shark, Orcas, the Catchalot (sperm whale), a Seal such as Sea Lions, one of the smaller toothed whales (dolphins) like flipper, or something else?