I personally prefer 1-4. At those levels, everything matters. At higher level, things start to average out a bit more, and no one is hanging on the edge of their seat for routine attack rolls. When one hit wit a high damage roll could drop a PC, it's very exciting. And I like when resources are limited enough that any non-cantrip spell is an important decision. Not to mention things go a bit faster when very few characters have more than one attack.
I'm currently running a game that has just reached level 19, and it's definitely still a lot of fun, but I wouldn't want to play at that level very often. It's big and epic and cool, but complicated and time consuming (though nothing compared to older editions, which were hell at high level). I've mostly been sticking to larger narrative decisions and a few big, important fights to keep things from getting bogged down, but I think that's what playing characters at that level should be all about. The minutia falls away in favor of the most important stuff.