I like rack pull-ups for two reasons.
1. I can do high rep work because my fat ass can't do that many pull-ups.
2. They target the lats more directly, you can really focus on them at that angle.
The one downfall is it's harder to add weight to them, you have to balance weight plates in your lap.
I usually do a couple of sets of chin-ups and then finish off with a couple of sets of rack pull-ups.