What's most important is reliability. The timetable is the face of the product. It has to be reliable, and it has to be on time. Then it has to be, of course, frequent. That's the next step. It makes no sense to have a train once a day or to have two trains per day, so you need a train every two hours or every hour. That's the important part. The next step, really, is to increase the speed to reduce travel time, because it makes no sense to have a very high-speed system with one train per day. I think that's obvious.
I would say that for speeds, frequency is a necessary condition, and if you have high speed, the frequency should ultimately be a result of it.