If durability is your chief criteria, a lot of riders swear by the Schwalbe Marathon Plus. I've had great luck with the "Panaracer T-Serv for Messenger Tour Guard", which are Kevlar (Aramid) belted, and are a great ride/tread pattern in addition to being very durable. I think they're pretty comparable to the Panaracer Pasela TourGuard recommended in an earlier post.