In my opinion, you should learn whichever one you want to learn. Yes, learning Modern Standard Arabic will make it easier to learn a dialect later on, but you don’t need to learn MSA to learn a dialect. It’s obviously a lot less effort to just learn a dialect than it is to learn MSA then a dialect, so if you don’t actually enjoy learning MSA, you could find it demotivating and wonder why it’s taking you so long to reach a level where you’d feel comfortable to start learning a dialect. The truth is that there is no level that you need to reach in MSA to start learning a dialect. 

You can also learn MSA after learning a dialect, which would be easier than learning MSA from scratch. That’s actually closer to the native experience, because we learn our dialect at home then learn MSA once we start school.

The point is that Arabic is one language, and no matter where you start, you can’t go wrong. So start with the one you will actually use and enjoy the most, and that’ll take you a long way.

Hello Ariana !

befor I answer your question , I'd like to say that your question is not stupid , in fact it's very important to answer this question before you start Arabic ! 

you will get many answer and opinions and arguments , Arabs themselves can be biased , and give you different opinions ! 

So, basically my answer is an opinion not a fact you should know that !

I have always been asked this question from people who want to learn MSA and dialects , they seem to be confused and they don't know what should they learn !

sorry o the long introduction I just want to be accurate : so , the thing is it depends on your goal first and on your situation meaning why do you want to learn Jordanian ? you should answer this question , if you want to live in this country you should definetly learn the dialect if not you should answer the previous question 

secondly , dialects are all connected to modern standard Arabic , they have developed from this language so it's the mother of all 

dialects , so if you learn MSA , you probably can understand many dialects , and you'll be able to pick them up , but if you learn one dialecrs only you'll have some difficulty to understand another , unless if it's similar like gulf dialects so it really depands !

however , Arabic is still used in the Media, Tv, Newsapapers , Articles online , books ; Novels , schools , universties ; in meetings ..and so on ..so Arabic is more an accademic language ..and almost all Arabs can communicate in this language and understand it ..so it's the lingua franca between Arabs !