You should stick to MSA because it is used in all universities media and magazines.
Using MSA will help you better in understanding the language as a language not as a street language. You ll also understand the media, read arabic subtitles, read and write perfectly, and attend a school and read its curriculum without a problem. If you learn the street language then you ll have to learn more than 5 of them.
I totally agree. Learning slang before mastering the standard language is a recipe for disaster. I live in KSA, here we have people speaking many different "accents" as they call it. I call it slang because "alem" means pain for some and pen for others. Watch enough movies and you can pick up street language. I don't think you can say that for MSA.