I started my zen practice with shikantaza. For a beginner, I would say I was doing really good. After 6 months, I got great personal transformation out of it.
Unfortunately, this small win caused me to slip and get lazy with the zen practice - I was looking for a shortcut. I started to think if I need any practice at all. This caused me to slip big and I was at square one after another 6 months.
When I had another attempt at it, it didn't went as good as with the beginning. I think I was doing the practice wrong, I thought I was doing it ok, but I was actually thinking a lot and I was not even that aware of it. It became a bad a habit. I lacked the ability to separate myself from my thoughts and trying to do an intense focus somehow mixed with those thoughts and it fueled a sort of negative energy state.
After realizing that mistake, I started the breath counting. And it was good, because I could easily benchmark whether I'm doing meditation right or not.
However, I was frustrated that sometimes I just can't hold my attention. I'm supposed to be counting, but I'm sinking in thoughts (I work as a software developer, my job requires me to think a lot). And then I reminded myself of shikantaza. And I felt it's just easier to focus. It's easier to stay present during the practice. I could cut thoughts at the first word rather than just observing thoughts. And this time I could tell if I was present and I could tell if I got distracted by thought.
I think that shikantaza is a more powerful method in our world full of distraction - but the practice of shikantaza is like a double edged sword, because unlike breath counting, it has no objective way to tell if you are doing it well or not. A person that is doing shikantaza well, knows it, but a person that is doing shikantaza wrong, thinks he/she's doing well. It's similar to how when you are awake, you know this is not a dream, but when you dream, you may think you are awake.
I think, doing breath counting for the first 6 months, then switching to shikantaza may be a good strategy - but then be really careful if you are really alert and objective. And if you think you were alert the entire session when you are just getting started, it's very likely you were unconscious the entire session. Also don't overdo it. After the session, relax. Try to be present, but relax. It's not possible to maintain that intense focus indefinitely.