This is one of the most asked questions, To make it clear for you. simply, the answer depends on your needs..
Why do you learn Arabic? If you learn Arabic to work or to communicate with a specific country, Dialect is the best choice.
But If you learn Arabic to know about Arabic Culture literature, and Islam, in this case Arabic Fusha is the best choice..
This is ridiculous. There are tens and tens of dialects, it does not make sense to learn one. For example, if one learns Lebanese, will he be able to speak to people of other dialects? no, because he is only used to Lebanese.
That is why, one must learn Fus'ha (MSA) because it is the universal Arabic that all Arabs in general can understand and should be proud to speak it.
Just like Muhammad wrote, it depends on the reason that you want to learn Arabic. If you'll write a little bit about the reasons that made you decide learn Arabic, you'll be able to get better advises about what would be better to learn.
Adi
