Publication order seems essential for the main plot's reveals, but I recently tried chronological with my kid and it changed the vibe entirely. We started with 'The Tales of Beedle the Bard' and 'Fantastic Beasts' before 'Philosopher's Stone'. It frames the wizarding world as a living history before meeting Harry. You get the lore's texture first, so when Diagon Alley opens up, it feels like you're stepping into a world that already existed. The trade-off is you miss the slow-drip mystery of what magic is—Harry's wonder is your gateway, and starting elsewhere can make his early discoveries feel redundant.
A friend swears by mixing them: read the main series in publication order, but slot the supplementary books in where they'd historically occur. 'Fantastic Beasts' after book 4, maybe. It's messy, but it layers in background during the darker turn of the series. Personally, I think publication order works because the books grow in complexity as you age with them—thematic maturity aligns with the release schedule Rowling followed.