For the speakers of European languages it is usually quite difficult to learn to pronounce correctly some of the sounds of Arabic. Turkish does not have any sounds hard to pronounce for Europeans.
The Indo-European languages and the Afro-Asiatic, including the Semitic languages like Arabic, are distinguished from most languages of the world by having much more irregular grammars, of the kind that was traditionally named "inflected".
Amazingly, while the more irregular grammars of the "inflected" languages are better seen as a bug and not as a feature, in the past the European scholars believed that such grammars are a sign of superiority of the Indo-European and Semitic languages, even if it is much easier to argue in favor of an opposite point of view.
In conclusion, I believe that for a speaker of European languages it is much easier to learn Turkish, due to easier pronunciation and more regular grammar.
Nevertheless, when there is no special reason for learning either of the languages, Modern Standard Arabic or Classical Arabic are more interesting languages from a historical point of view, enabling the understanding of many facts about the old Arabic literature or pertaining to the related Semitic languages that have been very important in the Ancient World or about the origins of the Greek and Latin alphabets (Standard Arabic has a conservative phonology and it still distinguishes most of the sounds for which the oldest Semitic alphabet has been created, which has later evolved into the simplified Phoenician alphabet, from which the Greek, Aramaic and Hebrew alphabets have been derived).