What notation style do you prefer/find easier to read?

For what its worth, since I am only familiar with the Yokoyama Dokyoku style notation I can only comment on that one. I like it very much , its very intuitive and provides a good connection to ones "movements".

Jon, interesting question and certainly reflects a fundamental difference in approach to learning the instrument between those who live and learn in Japan and those who do it in other places. It's not common here for learners to venture into other school's styles and therefore other types of notation. Typically, a learner learns from one teacher and moves along that path without too much question. In my case, I learned chikuyusha style, kinko notation first. My teacher thought it necessary for me to learn tozan style as well for which I am grateful as I have had many instances where reading it was necessary. Much after that, I adapted western notation reading to my abilities with the shakuhachi and after that, Yokoyama's style. Of all, I find kinko easiest because that is what I'm most accustomed to. Your question asks about the idea of the intuitiveness of its nature. When learning from a teacher, the notation is only part of what is transmitted. In fact, a great deal is transmitted orally as dictated by local tradition and isn't included in the written notation at all. As such, after a piece is learned, the notation becomes something of a mnemonic reminder of what was completely transmitted at the time of learning and my guess is that when learning that way, any style of notation will do.
But then, there are those who have no specific teacher and possibly learn from more than one, though less frequently. Do they see different styles as being inherently easier or more difficult in terms of learning, or is it all the same?

I am most comfortable with Kinko because that's what I learned. But generally I prefer Japanese notation to Western because it's easier on the eyes. If I didn't play Kinko/Jin Nyodo music I'd probably prefer Tozan because I think the rhythm aspect is clearer than in Kinko. Which is helpful in cases where the music has a specific rhythm.

There could be a lot of discussion about whether having more detailed notation (such as Jin Nyodo or Yokoyama) is preferable to skeletal notation (such as Watazumi's scores) but that's probably going to veer off topic.

Deep down I hate all notation because I'm not good at it! But I will say that learning Japanese notation carried a sense of accomplishment after decades of defeat at the hands of the Western stuff.

You're familiar with Tokuyama's notation I think. It is very close to Taizan Ha. HA replaces RI etc. Tokuyama is a little more longhand than the traditional Taizan Ha notation available from the Myoan-ji temple. However a few lesson with the traditional Myoan-ji system and it is pretty self explanatory.

There is some very good stuff in the Tokuyama repertoire. Enough to give most people a lifetime of work.

I think the answer to the question would often be the style of notation one has played after the most and most accustomed to. The same in my case. But I do like to read all kinds of other notation systems and the different approaches to solve the challenge of how to transmit a musical idea to others.

I must say that Tozan notation has taken a step further than most other schools in clarity due to the rhythmic aspect. But then again the augmented clarity has its expenses and Tozan notation may not feel as "free" for personal interpretation as other notation systems. But that depends on personal preferences to what is important.

Agreed! In my compositions I jettisoned western notation for graphic/time notation (pre-shakuhachi life), then would transpose it to western if others would be reading it. Shakuhachi notation - no matter the school or genre is fairly easy - compared to western notation, for me.

I'm not sure I've seen it, how does Tozan notation indicate rhythm? Are there any tutorial books describing it?

Here is an artificial score describing in one sheet the essential of Tozan notation. Rhythm is indicated on the right of the katakana, it's quite similar to western notation (quavers, semiquavers, triplets, etc.) I think the Tozan notation is very convenient to read. Its only real default is the distinction between large and small katakana, not always obvious to identify when you sight-read some hand-written notations.