Has anyone been to puerta vallarta in august or sept. Is the weather really hot and humid and did it rain alot.
Thank you

After April and until about June or July it will become increasingly warmer, to about 90° F or 32° C, and more humid (80°F - 27°C at night). Around mid June the rains begin. In the rainy season the humidity will increase during the day until the rain comes.
Normally, and I repeat Normally, it will rain for about 2 hours - very heavy with thunder and lightning - in the late afternoon, in the evening or sometimes in the middle of the night. It hardly ever lasts long unless there is a weather system of the coast.

It rarely rains 24/7. But yes August and September are the official "rainy season" and statistically the hottest and wettest months of the year in Puerto Vallarta.

Is it better to stay in the main part of Puerto Vallarta (specifically the Melia resort) or at Neuvo Puerto. This will be the first time for myself and my family to go to puerto vallarta.

It depends what you like and what you plan on seeing and doing. Out in Nuevo Vallarta are the newer, larger, more high-end resorts. The beaches are nice out that way, but besides that there's not a lot "to do".

The city of Puerto Vallarta has all kinds of hotels, from budget to fancy, but not many "resorts" more just real nice Mexican styled hotels. Also many condos available. I enjoy being walking distance to downtown, because I go out exploring for most of the day every day (when I'm not at the beach or beside the hotel pool).

So completely personal choice, depending on what you want to get out of your trip.