Levels and Curves
|Tool:||Levels and Curves|
Levels often deals with the black, grey, and white points of the image. Grey is the middle ground between when you set as "max black" and "max white"
Curves will typically be used to adjust overall intrinsic brightness (luminosity) or individual color adjustments (RGB).
While it's possible to achieve similar results using each, they are best suited in using Levels for manual contrast and Curves for better color tone control.
Ease of Use:
Scale of 1 to 5; 1 being easiest, 5 being hardest