ESTA is supposed to be a lower hurdle than a visa. But from what I've heard, approvals take longer and quite a few people get rejected.
Countries like to pretend they're still visa free, but honestly, it's just a pain in the ass and I'd rather they call it a visa. It's very, very easy to book a plane to a country, see all info indicating its visa free and you can just go, then right as you're about to head out, you decide to check for the 50th time just to be sure... and it turns out there's some "visa free process" for your country called EDtdjvubHHVJVF or some other random assortment of letters that involves a 2 hour application process and 24-72 hours (business days only) for approval results to come in. A visa would be preferable because it's more transparent.