What Should I learn: Ammiyah, or MSA?

"Should I learn Ammiyyah (colloquial language) or Modern Standard Arabic first?" 
This is a question that haunts most Arabic learners who don't know where to start. In order to answer this question, we define both parts of the Arabic language and understand what these two sections of the Arabic culture represent. This allows you to choose a learning plan that matches your goals.   

 What is MSA? 
MSA (Modern Standard Arabic) or AlFus'ha (الفصحى) is the official Arabic language. News broadcasts, literature, poetry, and every legal document in Arabic is written in MSA. As it is the official form of Arabic every Arabic speaker knows and understands MSA, no matter where they come from. However, we don't speak MSA! Instead we use dialect. 

What is dialect? 
In short, dialect is the spoken form of Arabic. Dialects are region specific; each country has its own dialect. Sometimes within countries dialects and accents vary. For example, in Syria we have a wide array of branches of our own Syrian dialect. While the majority of the population speaks the dialect of the capital, all regions have their specific accents and vocabulary. At times, you can tell where a person comes from just by hearing them speak! 

What is better for me to learn as a beginner? 
As a beginner, this information might be confusing. What you should learn solely depends on your goals as a learner. As we're rushing in excitement towards learning a new language we mostly forget to put precise and clear goals in place. 

"becoming fluent" isn't a goal, it's a wish. 
"being able to have a 30-minute long conversation about my day at work with my colleague by March" sounds like a clear, precise, and achievable goal.  

After you set your goal you should be able to see what suits you the most. Will you be reading books in Arabic? Translating legal documents? travelling all around the Arab world and speaking to people with different dialects? MSA might be your area of interest. 

However, if you're planning to walk in the markets, communicate with people and maybe spend time in a specific region then what you're looking for is Ammiya. 

One thing to keep in mind when it comes to Ammiya is the following: since it is a spoken language, there are no grammar rules in Ammiya. The languages of the streets of the Middle East were all built on the common official language MSA. 

Since there are no resources to teach ammiya grammar, the process of learning it for a beginner might be a lot more challenging. Yet, it is still possible to learn it through exposure to the language, its media, and its different patterns. 
On the other hand, Fus'ha thrives on grammar.. There is a rule for everything! This is why some teachers advise students to start by learning Fus'ha first. 

My opinion as a teacher is that a learner should be able to choose for themselves. Nobody knows what you want better than you do. So set a clear goal, focus on your priorities, find your teacher, and start learning! 
In your quest for learning, keep in mind these words of the great Nelson Mandela: 

"If you talk to a man in a language he understands, that goes to his head. If you talk to him in his language, that goes to his heart"