First and formost, Egyptian Arabic is a mix of Languages. In my daily conversation, I use Arabic, Turkish, German, English, French and pharaonic words. All the foreign words are key words that are used in the daily conversation. Now which one is the most popular, It depends.  If you want a career in Acting or singing, then other Arabs may consider learning the Egyptian Arabic.  If you're comparing the Languages in terms of pronunciation, intonation and so on, then definitely the Egyptian is the worst. I love the Eastern Arabic, that is the accent in Syria, lebonan, Jordan. The Gulf accent is awesome too. Sudanese and the west Arabic countries' accents are very beautiful as well. Now which one to learn, the MSA or one of the accents, well, both choices have their outcomes. If you learn the MSA, you will be able to read and listen to the news, some talk shows, hitorical drams and Japanese anime dubbed into Arabic. If you want to talk with people and understand them watch movies and drams, then you'd better learn one of the accents. If you speak with MSA, most people will understand you and respond, but don't expect them to use it with their friends or families. I hope I've helped you.

"popular" as in how many people speak it? well that would be Egyptian , spoken by 80 million Egyptians.

if you are asking about which is the one that sounds best , well almost everyone will say their own dialect is the most beautiful. 

I would say the Tunisian dialect is the most beautiful , only followed closely by the Libanese dialect. 

I would certainly advise you to learn MSA first , for the simple reason that dialects are not written languages , so most of them don't have good learning materiel , and they also vary alot in the same country. Also , if your aim is to communicate with most arabs , and say you learned Egyptian , it'll be almost impossible for you to understand people from Morocco or Tunisia. Though MSA is more of a written language , and almost no one speaks it in their daily life , if you are stuck when speaking with someone , you can always switch to Arabic , an almost sure way of getting your idea through.

When I said Tunisian is more beautiful , I meant that it sounds more musical. Also , the Tunisian dialect includes all the arabic letters , which is not the case in most mid-eastern dialects. A truly non objective view indeed , but that's my opinion :p 

Hello Sandji, let me tell you that I was in the same doubt (or maybe I'm still in) than you. It's really difficult to make a selection in which dialect or which kind of arabic should we learn.. When I started to learn I had many advised like.. you must learn MSA! and you don't have to!! I think there's nothing like that in other languages. So I looked up on my goals.. so I started to learn MSA, because i want to be able to read and to talk with people of any country. So I'm learning still learning MSA at the moment, after of it, I want to move to a dialect, probably Egyptian, because it's popular because of TV and music, and probably it should be very well understood in the rest of the arab world, and of course I would like to visit it, but of course, if I had the opportunity to travel to any arab country, i will study the basis of its own dialect in order to have a more confortable talking with native people there.

Thank you, Ahmed and Oussama, again :)

I now have a better perspective on the dialects and their origins :) 

Your advice has definately been an eyeopener. Its very useful indeed!