well, as you probably know, there are so many dialects of arabic, but mainly if you learn one of them, you will understand 95% of other dialects being spoken around you People don't use the standard traditional arabic "the one used in writing" in conversations..although I personally think it is the best one to learn because anywhere you go in the arabic world, people will fully understand you.."although I admit it would sound a little bit funny.." if you want to learn a dialect, i would suggest either the egyptian or syrian because they are widespread & most ppl understand them personally, i have trouble understanding lebanese, moroccan, algerians..speaking arabic, i guess it kinda depends on where you plan to travel or why you are learning arabic :) good luck

I'm totally agree with Radwa in some points.If u speak formal Arabic in the street,people will certainly laugh at u.Egyptian and Shami (Syria,Lebanon,Jordan and Palestine) dialects are the most intelligible dialects in Arabic at least for the Egyptian people.Just to be precise,if u intend to visit any Arabic country as a tourist,u'd better learn its modern dialect.That'll be very useful for u.But if u desire to study Arabic culture profoundly,I advise u to learn classic one .That'll help u read Arabic books whatever its original country.you'll be also capable of hearing the news which is not broadcoasted in any dialect but classic Arabic.Good luck!

i think it is better to learn the classic one cuz it is the basic arabic ,but modern arabic it is diffrent from country to another cuz in each country there are diffrent dialects of arabic