I don't know any Arabic unfortunately. They are completely different language families with only slight overlap in vocabulary, but beyond that I can't make a comparison. I would say it probably depends on what your language learning goals are, but turkish is super fun to learn and speak, and its super fun to travel in turkey or just to hang out in istanbul. You might also surprise yourself speaking turkish in China one day with some Xinjiang people as well :D
To add, knowledge of Turkish will also make it easier to converse in Azerbaijan, Uzbekistan, Turkmenistan and a bunch of other countries in the region.
To add to that, I learnt to basic-speak the now extinct language of Chagatai, because I know Turkish.
Turkish is also mutually intelligible with Uzbek and Kazakh - it's basically like English and Dutch.
Edit:- Learning Chagatai practically let's you speak Kazakh and Uzbek partway. Tried it in both countries, might work in other places like Kyrgyzstan and Turkmenistan too. :)
More than half of the Iranian population belong to an ethnic minority, and the biggest by far is the Turkish speaking one, the Azeri - it's something like 1/3 of the population as far as I remember. I don't know if non-Azeri learn Turkish from TV, but for a lot of Iranians it's simply their first language.
