I love all the level ranges for the different experience they give. Each one has advantages and disadvantages.
I hear a lot from my players that they consider 1-2 less fun for how fragile they are. Still a lot of good game memories, but I grudgingly admit that it's probably more fun for the GM than the players at those levels.
If I had to choose a favored level range, it would be "as high as you can get the campaign". I always start at 1 to 3 ish, because I love the trajectory of low to high level characters as they build their competence. But at high levels, it sometimes feels like the PCs are just unstoppable no matter what gets thrown at them...which really frees me up as a GM to throw insanely unbalances situations at them with the confidence that they'll at least be able to survive, and the gonzo ways they come up with to try and triumph are always fun.
The highest I've gotten a long term campaign to is 19th level, all they way from 1st. So I'll say the 16-19 level area is my favorite spot.