I always use CX File Explorer. Easy to set up, fast, free and without advertising. No cable connection needed (transfer using Wifi).
Earlier I used tools like Airdroid, Superbeam and alike. In my opinion this file explorer is the best available solution. In addition to that it adds a great tool to manage your files on your phone.
Access files on NAS (Network-attached storage):
You can access files within remote or shared storage like FTP, FTPS, SFTP,
SMB, WebDAV, and LAN. Also you can access your mobile dev ice from PC
using FTP(File Transfer Protocol).