I prefer 2D if both are done equally well.
There is a creativity and a style to 2D that is hard to replicate with 3D, and you can do more with shape language and silhouettes in 2D to differentiate characters and not have it look weird or wrong.
Plus, 2D has more of a timeless feel, and will hold up for much longer (maybe even forever), versus 3D that even if super well done for the time, will eventually start to look and feel dated and weird as technology advances.
And with as long as adult games are in development for, anything to make them look more timeless is an advantage.