Hey Anna, I have been to Cancun and stayed for 8 days before.. It is nice, but very touristy. Their business is the beach! So maybe that wouldnt be your best option. Although there, they do offer decent priced trips to the pyramids and exploring the jungle, but both are at least an hour or more trip by bus. There are a lot of restaurants, a nice mall, flea market, water park and a ton of great night clubs in Cancun. But the daytime activities are based around being on the beach it seemed like to me...the city comes to life at night.

Which ever you choose will be beautiful! Have a good time.. I'm heading to Puerto Vallarta next month, cant wait!!

well, it depends what do you mean by "I don't want to spend my day getting fried on the beach". If you want to stay at the resort, just go out in the city and do something, Cancun is ok-ish, but it will be mainly touristy stuff for tourist crowd. Around Cancun you can go snorkeling etc (e.g., Isla Mujeres), or go explore some maya sites (Tulum or Chichen Itza), there is obviously the night life as usual. However, anything that is within a day trip of Cancun will remain touristy/Walmart/McDonalds stuff...

If you are ready to be on the road during your week then you can explore a little bit less touristy sites

- Pyramids (Uxmal, Palenque, Yaxchilan (not many tourists there, but a great boat trip hoping not to get eaten by caimans))

- Nice cities like Merida

- A little bit hippie backpackers town (San Cristobal de Las Casas) with the usual backpacker stuff (language schools, artsy stuff, lots of bars)

- An absolutely outstanding boat trip in Canon del Sumidero (near Tuxtla Gutierrez

So a lot of stuff to do if you are willing to travel (on real Mexican buses with the authentic crowd, but you can also choose the ejecutivo class and be like in business class planes, those buses rock! the best bus service I have seen anywhere in the world!)

Anyway, Mexico is absolutely great place and especially in Yucatan the fruit juices of completely exotic fruits are just fantastic!

Instead of Cancun, consider going to Playa del Carmen - it is less American, no sky-scrapers. Using it as a base, you can alternate beach & chill out with amazing tourism: pyramides, underground lakes and rivers, colonial towns, biosfere reserve parks...as above and more.  Acapulco is nice, but given the choice there really is no doubt - go for Yucatan! and enjoy...

@Isabella indeed Playa del Carmen is nice and has the advantage over Isla Mujeres that transportation is easier to mainland places

I love the comment of Justdoit about "Americans" (even though I call myself quite often mistakenly the US people Americans)

For those of you who speak Spanish here is a hit that characterizes pretty well the situation (Los Priosioneros, they have awesome texts!):

The text:

http://www.sitiodeletras.com/mostrar.php?lid=15259&artista=Los%20Prisioneros&titulo=Latino%20Am%E9rica%20Es%20Un%20Pueblo%20Al%20Sur%20De%20Estados%20Unidos

The group in action:

http://www.youtube.com/watch?v=2y6f8ksXZZw

Hi Anna, lucky girl!

I've been in both - Cancun and Acapulco. Both places have its ++ and --

Tourist service and infrastructure in Cancun are way much better developed than in Acapulco. But Acapulco less expensive. And it's more like real Mexico.

You can do some online "home work" on these places and compare them.

I just want to warn you, sorry. But watch out the weather.

You are going there during the hurricane season. It can be very stormy, waves can be so strong and high that it^ll make impossible to come close to the water. So you may spend your beach hours by a hotel's pool.

http://gomexico.about.com/od/healthandsafety/a/hurricane_seasn.htm

the advantage: since it is not a tourist season, everything's sells for a discount price  

cancun playa del carmen :) great !!!! i recommend

Playa del Carmen - way less touristy, but still backpacker buzz and nr Tulum ruins

Just was in Yucatan in April- loved Tulum, which was still soooo nice even 8 years had past since the last time 2001 when I spend New Year there...

Pristine beaches, small hotels, nature reserves, the ancient city of Coba...Maya temples. If you like sweetwater, there are large number of cenotes located in the Tulum area with names to dream of such as Maya Blue, Naharon, Temple of Doom, Tortuga, Vacaha, Grand Cenote, Abejas, Nohoch Kiin and Carwash...Bring your snorkeling gear! And enjoy!

I've been to Cancun, Conzumel, Playa del Carmen, and Puerto Vallarta. Out of them all I would recommend Playa del Carmen first and Perto Vallarta over Cancun and Conzumel. Cancun is just like going to an American city on the beach. Cozumel use to be wonderful but has turned into a mini Cancun with better snorkeling. Playa Del Carmen is cute little villlage and Puerto Vallarta, older and bigger city with a number of thing to do. However Puerto Vallarta's beaches are not as nice and can have bigger waves.

So nice to see people like my country :-)

The opinion of a Mexican: go to Akumal and from there visit all cultural and natural places, from Mayan ruins to diving pits and pintoresque towns...

Send me a message if you'd like more specific recommendations...