guys please you should understand this

when someone learn specific dialect like egyptian ... etc then he can't understand the other dialects example:
البنت بتعيط
"In egyptian means the girl crying and in syrian the girl yell"
but when he learn the standard arabic then he can talk and understand all the dialects,
example:
الفتاة تبكي
الفتاة تصرخ
it's understand between all arab.
of course, learn dialect will be useful if the person wants to live in a country or for some reason then he learn the dialect that country it's help him to communicate with the people of that country

You can pick the dialect easily because you're a native speaker, to a foreigner it's not as easy as you may think. 

If someone is learning MSA, then he/ she shouldn't watch movies, because there's no movie in MSA, ALL of them are in dialects. 

Books are difficult to read for people at beginner~intermediate level, I'd recommend reading children's stories only. 

فيه يوتيوب - فيه كل حاجة
الفصحى ممنهش فايدة

pick the dialect easily afterwards
listen to Arabic movies translated in your language???

Most people perfer to learn MSA Arabic and Arabic movies useless for learning

i think the most common dialect is egyption ones because you can hear it eveywhere specially egyption movies