Style 2 offers the most balanced user experience, making it easier to understand both the document structure and the current page content without overwhelming the reader.

I tested all three samples, and Style 2 is the clear winner for real-world use. Style 1 forces too much reliance on the Page Directory alone, which feels disorienting on deep technical topics. Style 3 gives full hierarchy visibility but sacrifices in-page navigation  a real problem for long troubleshooting articles with many steps.
Style 2's 3-level sidebar plus Page Directory combo means I always know where I am and can jump straight to the section I need. It's the same pattern top-tier docs sites Stripe, Microsoft Learn use for a reason it just works.

i prefer style 3

I prefer Style 2.
It offers the most balanced and efficient navigation structure.

I prefer Style 2 — Left: 3 levels + Right: Page Directory.

I like Style No.2

I prefer Style 2. In my honest opinion, it's the best balance of hierarchy depth and in-page navigation.

Style 2 I would like

I prefer Style 2. It provides a good balance between navigation depth and page readability. Three levels in the left sidebar make it easier to understand the document structure, while the Right Page Directory is useful for quickly jumping between detailed sections within a long article. It feels more practical for technical documentation with multiple topics and sub-sections.

Style 3 looks good for me