Which of these languages should I start to learn?

Arabic isn't too hard, you just need time to get the hang of the writing system. The problem with Arabic is that you should choose a specific dialect if you want to speak and not just read. And it's hard to find cles/resources for learning specific dialects (except maybe Egyptian, and this is one of the most widely understood dialects due to music and TV). What they teach in schools is Modern Standard Arabic which is for reading/writing and for communicating in the news and political discussions on TV, etc throughout the whole Arab world. It is not spoken natively by Arabic speakers and is a little awkward sounding when spoken in daily life.