The cities I liked the most were always Slateport due to its closeness to the beach, the museum, the market. It just has the charm of an older style village. Another was Lilycove as it is more of a modern version of Slateport and has the beach, my hideout, the megamart and my berry patches. I mostly find myself between Mauville and Verdanturf though, training through daycare and rematches, breeding and hatching eggs as its simply a long path.