The Most Comprehensive of Languages.

Arabic does enjoy certain characteristics unique to it among the Semitic languages, the most important of which are [*]:

1. It has preserved the sounds of the Semitic alphabet better than any of the other Semitic languages; it includes all the phonemes of the other Semitic languages (to the exclusion of perhaps two or three, about which there is doubt whether they are actually Semitic in origin), and also has extra phonemes that do not exist in the others, such as the thaa' ث, the dhaal ذ, the ghayn غ, and the daad ض.
2. It has the most extensive and precise grammatical and morphological system; all the grammatical rules in the other Semitic languages have their equivalent in Arabic, while there are many rules and phenomena in Arabic that do not exist at the same level, if at all, in the other languages.
3. It has more roots and lexical items than any of the other languages.

[*] Adapted from Fiqh al-Lughah by Dr. 'Ali 'Abd al-Wahid Wafi

http://arabicgems.wordpress.com/2006/03/04/more-than-a-dot-on-the-horizon/



 Ibn Hazm had a list on the criteria of a language being the best of languages. 

Ibn Hazm says;

..the most comprehensive of all languages, the clearest in expression, the least ambiguous, the most concise, and the most extensive in vocabulary to comprehend the names of all things, whether substances or accidents...

The 5th chapter of Ibn Hazm's Ihkâm fî Usûl al-Ahkâm. It's original title is: "The Origins of Language: Divine Providence or Human Codification".

 Looking at Dr. 'Ali 'Abd al-Wahid Wafi's discussion above, it seems that the Arabic language fits such a criteria.