I am often asked this question, so I thought about sharing my thoughts in a discussion, and I invite all Arabic teachers and students to share their opinion as well.
First it's good to point out that there is no right or wrong answer to this question it depends on what you hope to get from the language. I will try to present the pros and cons of each.

Advantages of learning standard Arabic:

- Plenty of online resources and well defined grammar rules. You have a wealth of books and online resources, blogs, websites and Youtube videos for learning standard Arabic

- It's understood all over the Arab world

What you can do with standard Arabic:

- You will be able to understand news broadcasts, read news articles, books, literary texts, the Quran since most Arabic written material is in standard Arabic.Some people make it look like standard Arabic is a dead language and no one uses it, but I don't agree to this. It's widely understood and it's used for almost all written Arabic material, news bulletins and even dubbed cartoon movies. It's just not suitable to use it for daily life conversations and may sound weird.

- Your knowledge of standard Arabic will be a very good foundation to learn a dialect later on. All forms of colloquial Arabic were derived from standard Arabic, All dialects evolved by adding transformations to standard Arabic, so learning standard Arabic makes it much easier, I believe, to learn a dialect later on. but not the other way round. If you have the dough, the onions, the cheese, peppers and mushrooms, you can make a pizza. but if you have the pizza it's very hard to go back to the basic ingredients. So your standard Arabic will be a very good foundation to start learning a dialect.

Learning a dialect:

- "Not enough online resources" I heard this comment from many people trying to learn Egyptian Arabic

- No well defined rules because we learn these dialects as kids by listening to people talking around us so there is no formally documented grammar, no standard way of writing, And so the best way to learn a dialect is to talk with native speakers.

- Some dialects are well understood in many countries while others are not. Egyptian Arabic for example is understood well because of the widespread of Egyptian songs and movies in the Arab world. I think this goes for Shami Arabic (spoken in the levant countries like Jordan, Palestine and Syria) and gulf Arabic. While some dialects are hard to understand for most Arabs like Maghrebi Arabic (spoken in Tunisia, Morocco and Algeria, and also known as darija) which for many Arabs sounds like a totally different language almost impossible to understand.

Advantages of learning a dialect:

- It might be easier than standard Arabic because standard Arabic has a complicated grammar, most dialects ignore a lot of the complexity in standard Arabic. so even though in standard Arabic the path is well defined, it's not easy, needs a lot of patience and determination. and it may take years to master the language

- Being able to communicate with people in daily life conversations

My opinion:

Learning a specific dialect only can never convey the beauty of Arabic. it's a language with so much logic in its grammar. I hear this comment a lot that Arabic sentences and language constructs are so logical like math equations. It's a language with a real philosophy behind it. One of my students wrote this in one lesson feedback "There seems to be a 'science' in the Arabic language." I was really happy with this comment because I felt I could make him see it. Learning a dialect directly is probably easier and more practical but I think it will not really make you understand how the language works, which is the best thing about learning a language. Being able to see how other languages found a different approach to expressing ideas.

What do you think?