Fondest memory: The beach between the Zona Dorada and town is often called "the locals' beach". It's rockier and less crowded, and sometimes you'll find a few locals catching a bit of wave action on their surfboards. It’s a nice place to go for a walk if you want some peace and quiet and a break from the tourist crowd.
The sunshine is definitely my fondest memory of Mazatlan - it works wonders for the gloomy, crabby personality that slowly takes over my mind after months of dark grey days in the Pacific Northwest winter.
The "Zona Dorada" (Golden Zone) is where you'll find the best sandy beaches, but also the most expensive, most touristy hotels. There are plenty of good places to eat and drink, plus locals on the beach offering sailboat rides, parasailing, hair braiding, etc. That said, Mazatlan's still not really like resort towns (like Cancun), so if you feel like you need that kind of distance from the local culture, this isn't the place for you. I enjoy it here quite a bit, and I'd also highly recommend getting out of la Zona Dorada and into the regular town to expand your travel experience.
Favorite thing: What can I say ???? It is great to relax by the beach, catching a few rays. In January, the water was a little brown. I guess at that time, a storm stirred up the water. The water was not as warm as I expected either. It was still a great place to hang out and people watch