The smudge is one of the effects very easy to do that, if done right and with the right Brushes, can give very good results creates depth and softens the colors.
Here I bring you a compilation of the best sets of Brushes for this purpose.

Cloud Smudge Brushes

2nd Smudge Smudge Brush set

Smudge Brush

Smudge LadyTorr’s September 1

SimpleSmudges

September Smudge

Basic Smudge Brushes