No, everywhere is dangerous! I believe this answer really depends on you! What are you doing?  Who are you involved with?  I am from Iowa and let me tell you …you can find PLENTY of trouble in my wholesome state!  You have to treat Mexico and ANY place you travel as you would anywhere else and that is always with precations! My grandma says nothing good happens late at night..lol  Well for me as untrue as that is for me it does have lots of truth to it too.  Are you walking alone at night?  Are you with people you trust? Are you involved in illegal activities?  I have driven across 18 states of Mexico and I have now lived in Mexico for 5 years and I have had some scary moments but that is life no matter where you go.  Nothing that would stop me from visiting or living in this beautiful place.  Travel safe, that is the key. 

When in Mexico or any country for that matter I always encourage to spend in local currency. Besides the fact that you get to see and “experience” the money you also get better prices.  This also is a better way for you to negotiate.  In Mexico it is normal to negotiate, it is a part of the fun. You look and seem more “local” when you carry pesos.  Here is a video I made with more info!

I personally think from the mid of November till about mid-April.  This is the least humid and usually between 75F to 85F.  After April it begins to get humid and I am used to it but some do not like the humidity.  You will pay the price as those months are our HIGH season.  If you don’t mind humidity, like me, you will enjoy to cool off in the ocean and/or the pool! 
 
Rain:
Do not freak out! The rain here USUALLY is for 15 to 20 min and then bam the sun comes out.  Where I am from in Iowa we have rainy days and I think that is why many freak out when they see it on the weather forecast for the Cancun area.  We are in a tropical area and it’s typical to have a pop-up kinds of rain storm.  June to October it is more likely to have more rainy days but still not as often as we might expect in areas of the US.