Do you mean which dialect? I think it depends on a person's needs and intentions. I intend to communicate with  people in Saudi so I am learning that dialect but if someone wants to learn how to read and understand formal literature and media like the Qur'aan, newspapers, news etc they should learn Standard Arabic. Obviously, Egyptian is the biggest Arab dialect so it too is worth learning. 

when I started learning Arabic, I started learning standard arabic, but after a few months of watching Egyptian movies and series, I kind of feel the egyptian vocabs and grammar are replacing the standard ones in my mind, when I want to speak or think in arabic, it's easier for me to do it in egyptian dialect!

anyway, I'm trying to learn both, because I know both are important

P.S: I was browsing the web, when I accidentally found this page and this site

it sounds like a great and useful site, I wonder why I haven't found it before, I hope I could get the help I need in learning Arabic here and also help others who want to learn my language

I don't have a pref, as a beginner I watch video to learn , most of Them are Egyptian, and some standard arabic I think, in general I want to be able to communicate ! I think Egyptian dialect will win.

What's the difference?Accents?