For Druid, it really depends on your goals and playstyle.
Levels 1-13 is pure and utter misery no matter how you slice it.
At 14, you obtain your first animal Charm. This line alone is more than enough to take you to 60 with startling efficiency (especially with access to a
GGR.)
Your first quad AOE doesn't show up until 34, but it opens another viable route to solo to 60.
Don't care about hitting 60? Hit 29, and get an invite to Dial a Port! Each spell level thereafter increases your plat-making opportunities, on up to 57 when you'll get the odd request for a Succor through Siren's Grotto.
In the end, the only universal constant is level 56, when you finally unlock
Wake of Karana.