I've been to Puerto Vallarta a couple of times.
1. It will most likely be humid
2. Depending on what you do, you will want something flexible at least - landscape (from boat?) and zoom some scenery - arches. Some may be from a distance some may be up close.
3. The streets/roads can be dusty - depending on the rain. I don't think its the rainy season... that's typically fall.
Easy recommendation to start: DA 18-135mm WR ( or 18-55mm WR) at least. Take a wide/fast prime, but you'll probably spend most of the time with a wide angle. If the 16-85mm WR is out, it may be worth a shot.
For the 'downtown' and port (they have a WalMart now
) - somethink in the range of 14-28mm would do well.
I guess if depends on what you do during the day/evening.
If you want to try something unique - take a bus trip to Punta de Mita. You will get away from the tour sales, and find a nice / clean / quiet beach. Its ben + 10 years since I've been to that spot... but its next to the 4 Seasons and St. Regis
. There are a lot of boat trips that go to places south of Puerto Vallarta - great days in the sun, all the tequila you can drink. Some even have night shows/dinner combo.
Its pretty much 2 cities...
The 'newer' city to the north of the cruise ship terminal (new Hotels/condos/WalMart/shopping mall)
The 'older' city to the south of the cruise ship terminal (older hotels/condos/timeshares down until you hit the shopping district - 'Senor Frogs') - most of the shopping tourist stuff ends at the 'river'.
If you have a condo - groceries are (were) cheap - at places like Mega. I'm sure that its changed