First it was druid, but the animal forms are so weak and 95% of spells are concentration, meaning you basically ignore all of them in favor of moonbeam/flame sphere 99% of the time. Huge disappointment with druid.
But then again, huge disappointment with warlock and the eldritch blast+hex spam gameplay.
Druid I agree with. By limiting use of concentration spells in animal form, they utterly eviscerate any enjoyment in the class compared to the standard TT rules. Warlock though, that's what they do at lower levels. You get more interesting options as the game goes on, and frankly, if long resting weren't so easy, they'd also have some comparatively strong options over the course of an adventuring day.