What is the difference between fish oil, krill oil, and coq10? Which is best for a healthy person to take?

Don't take any. A healthy person with a satisfactory diet does not benefit from any of these supplements. It may be useful to eat a diet rich in fish for long-term prevention of cardiovascular disease, but even this is uncertain. Fish and krill oil are both marine oils rich in omega-3 fatty acids that may help some people with heart or vascular disease.