I think the most relevant is through your network, mainly because it’s generally a trust matter on both ends. It’s best when the deal is a known quantity vs looking over “who’s hiring monthly HN posts”.

I had 10-15 people i was working with (not all employed) at my last startup and they all came through my network either directly (ex colleagues) or through trusted parties.

Again it’s mostly a trust thing more than anything.

I think a good strategy is to get close to the kind of startups you care about without (before) direct intent to join. It’s easy to hang out (or at least it used to be) through various events, meetups or co-working places.

Many startups I didn’t join and could have been good, I’ve met through open-source (Hadoop, HBase, Mesos, etc.) these are companies like Cloudera, DataBricks etc. when they were tiny. I still miss that crowd, years later.

So it’s mostly a matter of being close to what’s happening, able to filter and ready to jump when opportunity arises.

Look for startups that interest you and then email the founders. Follow up every two months until you hear a hard no. Things are absolute chaos at an early startup and it's rare that the job board (if even there at all) is up to date.

Source: I work at an early stage startup.

Y Combinator and other accelerators have job boards: https://www.ycombinator.com/jobs

A lot of VCs also have job boards, or they will list their portfolio companies and you can reach out directly:

https://jobs.a16z.com/jobs

https://jobs.sequoiacap.com/jobs

https://kindredventures.com/portfolio

etc