I'm also looking for an answer to this question, and I've found interesting comments from people here, in ResearchGate, about this point. It seems to me that Mendeley is the most recommended one. Check the discussions on the links below:

https://www.researchgate.net/post/What_is_the_best_way_to_organize_collection_of_scholarly_literature_pdf

https://www.researchgate.net/post/Which_reference_manager_are_you_using

https://www.researchgate.net/post/Which_free_reference_management_software_would_you_recommend

https://www.researchgate.net/post/What_is_the_best_reference_management_software

https://www.researchgate.net/post/Wich_software_did_you_use_for_references

Just one more tip! Don't forget to visit the RG Topics below, where you can find many questions and answers that may help you:

Bibliographical References (33 Questions ; 72 Followers)

https://www.researchgate.net/topic/bibliographical_references

Bibliography Manager (15 Questions ; 26 Followers)

https://www.researchgate.net/topic/bibliography_manager

Reference Management (12 Questions ; 7 Followers)

https://www.researchgate.net/topic/reference_management