My first visit to Mexico was to Puerto Vallarta about 25 years ago and have been there so many time I lost count a long time ago. My first advice is to not get sucked in by the timeshare people and the easiest way is to already have airport transfers. Trust me if you want to do a timeshare presentation you will have plenty of opportunities as they are all along the streets. If you want to shut them down quickly my response is usually that I am leaving tomorrow #sneaky. If you want to stay at your hotel most of the time (not my way of traveling) then you might like the marina district with the fancier hotels. I prefer however to stay in Old Town just over the river on Playa Los Muertos.
My favorite hotel is the Playa Los Arcos. It is right on the beach, has a pool with easy beach access (nothing fancy, maybe not the best option if you have little kids). it is a short walk either along the beach to the Malecon or through town and over the river. If you go the beach route stop at the Day Off Beach Bar for a margarita or 2×1 beer. If you go the river route make sure you visit the Cuale Island Flea Market under the bridge for local handicrafts (bargaining is expected but be fair). A short walk past the bridge on the left you will find La Casa de la Vainilla, I never leave without a good bottle of pure vanilla. A Old Town must for mojitos and fish tacos is Joe Jacks Fish Shack – try the ginger or pineapple mojitos. For a dinner overlooking the Malecon go to Bar Oceano Restaurante and ask for a table on the second floor balcony. If your trip to PV is for a special occasion then you must visit El Panorama, it is on the top of the hill with the most amazing views (you will need a reservation).
I am not a fan of the standard snorkeling tours in PV, mainly because I prefer the Caribbean side of Mexico for that, but you should still get on the water and the best way to do that is by sailboat, a cruise to the Marietas Islands is perfect. If you do want snorkel then it should be with the wild dolphins, keep in mind these are animals in the wild so there is no guarantee you will see them but if you do its a once in a lifetime experience.
One of the best reasons to go to Puerto Vallarta is for the adventure and fun you can have. You cannot take a trip here without doing the Cuale Mountain Expedition, this tour is full of so many different adventures packed into one full day of fun! You will start with a hike through the jungle, first up if a thrilling zip line ride over an expansive gorge. You will walk across a canyon on a wire then rappel 90 feet off a sheer cliff. Climb back up and then experience a free fall 80 feet to a path before riding a zip line into the river below. From there you will tube down the river to meet your mule who will carry you back up the mountain where the tour ends. After the tour you can relax in a hammock, have a drink or lunch at the restaurant. Make sure you try some of their tequilas and I highly recommend you buy the video of your tour. Your photos will be so much better than you could have taken (all below taken by the tour photographer).
Happy Travels