Having lived (and played) in both, crawl spaces are more user friendly for some types of repair and additions. Although there is usually away around anything. I did recently see a slab house where the owner had put redundant systems under the slab. (ie he ran extra supply plumbing and an empty wire conduit to several locations). I cant deciede if this was stupid or brillaint until he told me he had to turn over a supply line to his bathroom sink.