Help With Cache Options

I'm sorta lost when it comes to caching with Panels as it seems when I enabled caching it shows the same thing for every node.

Example: setting the body to "simple granularity:none" showed the exact same content for every node!

Then I fooled around and set the simple caching to context, which seemed to work.

So I suppose panels that get changed (body, title, author) would use context caching?

And maybe panels that are site wide (header, menu, ads) would be set to granularity: none?

What about ajax blocks? Set them to none? (blocks for popular content, trending etc).