Hugo predates those two. It got its first tagged release almost a year before Metalsmith and two years before Lektor.
2. Modern
I feel most comfortable with pelican but with huge sites it gets kind of slow.
Everyone has different needs and tastes so no tool works for everyone. Here's how I see Hugo's strengths and weaknesses. I'd love to know what other people see are Hugo's strengths and weaknesses.
Hugo's key differentiators: 1. Ease of install 2. Speed (critical for large sites) 3. Integrated live-reload while editing in near realtime 4. Multilingual capabilities 5. Flexible 6. Very strong community 7. Very good & comprehensive documentation (but not perfect...yet)
Hugo struggles with: 1. Not integrated with Github like Jekyll (though webhooks solve this to a large degree) 2. No plugin support 3. Media & Asset processing not tightly integrated
There are many solutions that work around Hugo's limitations, some which are quite elegant, but at the end of the day they are workarounds and require external tooling.
We would love to address these weaknesses in upcoming releases as best we can. If you are interested in helping we would love to have help.