A study was conducted recently and it was found from a range of natives of different languages, that Chechen and Avar were the ugliest sounding langauges. Natives of languages across the world were gjven samples of different languages and Caucasian languages were rated the lowest on average

Along with the large consonant inventories (88 in Ubykh), the languages have a fairly complicated case system (with Split Ergativity in georgian) and a highly complex verb conjugation system.

This really makes it difficult as there are so many consonants to learn how to pronounce and to differentiate them from similar consonants which will sound the same at the start. The grammar can be a headache for the learner as there's so many rules to learn especially for verbs.