In my opinion, the second volume of Maus (which shows Vladek trying to stay alive day to day in the concentration camps) is the better and more effective of the two. The story is dark and very chilling, and we cannot stop reading Vladek's terrifying story, wondering what will happen next. Mixed with this are the excellent elements of Vladek and Art's present lives and interactions with each other.
Maus is a truly beautiful story. Don't miss it.