Syrian and Iraqi dialects are definitely the closest to MSA. Iraqi dialect is probably the one that respect MSA's grammar rules the best, due to the fact that the most influential grammar schools (Basra and Kufa) were based in Iraq.

I heard that to find out where people from, you don't ask where they are from, you ask them which dialect they think is closest to MSA. Ha ha. My teacher says the bedouin in Iraq speak Classical Arabic.

At first I Arabin ... I think that the Arabs speak with one vernacular language .....

I just answered the question and pick Saudi dialect , but I want stress that every body will be proud that his/her dialect is the closest to MSA , so actually you will not find a one answer. every one will claim that his/her colloquial is the closest. to read more about this is useful debating link. http://forum.wordreference.com/showthread.php?t=615365

Saudi (white) dialect