it depends many things... where you would like to work?  what kind of job you are looking for? for example if it's about translation, so for sure MSA is the best for you, but if it's a job that needs contacting with others, and to live in the country so it is all depends on the place you would like to move to. 

good job opportunities are in Dubai, Emirates, Qatar, Saudi Arabia, Abu Dabi. The dialect of these countries is Gulf dialect. and also there are  good opportunities to work in lebanon, they talk lebanese. so you'll need to study lebanese dialect. 

I find that all levantine dialects are so useful to learn and everyone can understand them, also Egyptian and gulf dialects are understoodable too.

It's all up to you. but if you attend to be a translator then MSA is the best for you. good luck ! 

Interesting, I can say all people that I've talked in italki were so nice.

But in reality, it's different. A lot of people act in this way and being judgmental, it's uncomfortable. But unfortunately that these people are exist, so all you can do is just to ignore them. And the most important thing to do is "to remind yourself that you'll never be able to go back being 5 years old and learn the language as a native speaker, and they too. So everyone of us is perfect in a language that the second is not.  And it is not the fault of anyone of us. It's the excitement itself. So just enjoy it, and enjoy your imperfection in this language, and be satisfied of your great achievement. And ignore those that will try to make their best to figure out imperfections in others. 

Enjoy it :)