Really depends of the species of pipe you are considering. Alligator pipefish, for instance, are more like sea horses and like a lot of vertical space (and cooler temps too). They hitch imitating floating grass blades and wait for food to come to them for the most part. Blue lined pipes are always on the hunt and swimming among the rocks so more horizontal space with rock work would be more important for this species.
If you could tell us what kind of pipe you are interested in and what kind of set up you want to have (reef, species dedicated tank, ect) you will probably get more specific answers. HTH