I'm going to Mexico... where should i go?

I'm going to Mexico for 7 days... march 15 - 22, I never been to Mexico so I'm not really sure were i should go. I'm 18, so i do want to party a lot, but sometimes i would like to sit down and relax a bit. Have any recommendations of nice places?

and any recommendations of the Caribbean's

Puerto Vallarta is the best for fun and has great beaches and hotels.
Cancun is more expensive and smaller.
I personally like Mazatlan.
About the Caribbean, I have been to Dominicana but it is def. not as nice as Mexico

I think Puerto Valletta would suit your needs quite nicely

cancuns beaches in my opinion are a little bit prettier than puert vallarta
but cancun is more expensive
obviously, if you know when you're going, you know WHERE you're going also soo idk how i can help you, mexico is big

If you're interested in Caribbean, I suggest punta cana. We stayed at the Bavaro Princess and loved it. Lots to do. Can relax and party both. If you want to do an excursion I suggest the safari and zip line which is new. If you email me I can send you some pics. Beautiful scenery.

For partying i would say Mexico City ( because it has one of the best nightlifes in the world, i think its event better than NY)
and Cancun.

For relaxing i would say Cancun, Acapulco, or Mexico City.

On the Pacific side, Cabo san Lucas

Plya del carmen is perfect.Small, good shopping, excursions,can party too. Fun to go to cozumel by bus or ferry.Always stay with some one else.Girls should stick together.(That's the grandmother in me ) It is safe just have fun where ever you go.