Kerning and tracking are both very important when it comes to typography in design.
Kerning is manipulating the space between two individual letters. This mainly becomes necessary for titles and headlines as these words tend to be larger and therefore the space between letters is more pronounced.
Tracking is the space between all letters. This is mainly used for body copy as one would be removing or adding the same amount of space between each letter in a paragraph. This is because it is less precise than kerning.
Which do you think is more important? Kerning or Tracking?