Pick one platform. Write it down.

This takes two minutes if you are honest and two weeks if you are not.

The question is not where developers should be. It is where the people who could hire, promote, or refer you already spend their time, and which of those you can stand to show up in every week.

Those are two filters and both matter. A place full of the right people that you dread opening will lose to a place with fewer of them that you actually visit. Consistency beats reach at this stage, because you have no reach yet either way.

If you are torn, the tiebreaker is not reach. It is friction. Which one can you post to from your phone in four minutes, on a bad day, without opening a new tab and psyching yourself up. Pick that one.

For most developers reading this the honest answer is LinkedIn, and the reason is unglamorous: that is where the decision makers are. They are not on Hacker News.

The one mistake is treating this as permanent. It is not a brand decision, it is a focus decision for the next ninety days. You can change it in January. What you cannot do is run three of them at a third of the effort, which is invisible in all three.