I still like Mazatlan (even after Zihuatenejo). I was there in 1991 with Kara and by myself in 1996 and 1998. It is a good size city with a resort strip to the north. The city itself has a good size market and is a nice place to wander around. We encountered a number of Mexicans vacationing there... not entirely gringos. Mazatlan is a place to find excellent shrimp dinners. The resort strip is fairly laid back with some degree of nightlife, I think, but that's not really my thing.
The sunsets there are consistantly gorgeous.