Is it easier to remove upper or lower wisdom teeth?

Upper teeth. Typically, upper wisdom teeth come out easier and cause fewer problems in the post-oeprative period. Many people experience very few problems with the uppers or lowers after removal, though.
Both can be hard. There is no correct answer for this. There are difficult cases involving both maxillary (upper) and mandibular (lower) wisdom teeth. With that being said, maxillary third molars are generally more straight forward.
Wisdom teeth. Typically upper wisdom teeth are easier to remove, heal faster, and have less incidence of post-surgery complications (ie dry socket). However, everyone has their own anatomy and there are exceptions.