Tukey’s HSD is the way go if you have a large number of groups (say, six or more) and you want to make all possible comparison. The downside is that it tends to be somewhat conservative with respect to Type 1 and Type 2 errors. On the other hand, the N-K can be a bit too liberal. Tukey’s Wholly Significant Difference(WSD, also known as Tukey’s b) tries to be like Momma Bear, and be “just right.” If you have k groups, use WSD if you want to do more than k-1 but fewer than k*(k-1)/2 comparison; otherwise, use the N-K.