So what's the right indent: 2 or 4?

A principle you often see mentioned in a Perl context is TIMTOWTDI (pronounced "tim toady"), short for There Is More Than One Way To Do It. I think some take it too far on occasion, using it to justify alternates which are objectively meritless, while I believe it means 1) one should be tolerant of differences and maybe even learn from them, and 2) adjust to what's best based on context.

With that in mind, anything that might be claiming to be an official style guide is merely making suggestions. So while your answer is inherently unanswerable, I'll leave you with the following:

From what I've seen, 4-space indents is by far the most common indent used, so I recommend that you use this. You will also come across 4-position tabs and 2-space indents pretty often. I use something I haven't see anyone else use (for somewhat historical reasons), so I won't mention it.

There is one "rule": Be respectful of the conventions of projects to which you collaborate.