In AD&D I got the most enjoyment out of my players having characters of 5th+ level.
In BECMI it was roughly the same, 5th+ level, but oddly more satisfying at higher levels relative to AD&D.
In both the above cases I use "+" rather than specifying an end to the range because in AD&D 100th level characters played just fine, and I didn't mind transitioning to Immortal rules after a nice long campaign had reached Master levels.
In 3rd/3.5 I would start players at 5th so their characters wouldn't die from a single critical hit delivered by an orc, and the mechanics of the game would collapse around 12th level - but my preference, to be honest, was to play other games instead.
In 4th, I'd have to say my preferred level range would have to be 1st-7th because those were the levels my group played through before the game not fitting our style became unignorable and soured the game for us.
How does all of that translate to 5th edition? I have genuinely no idea because I haven't had enough campaigns reach completion, and all the "how it used to be" doesn't mean diddly since the game is designed differently on a fundamental level.
I can say, though, that every level at which I've run 5th edition has been great fun (1st through 9th so far), and I see zero indication that the remaining 11 levels (and beyond, via epic boons) will be anything but fun.