USB Mass Storage (sadly, mostly deprecated on Android 4, 5, etc.).
MTP, and I know its benefits (a lot) and its weaknesses (browsing on a MTP drive with Windows Explorer has poor integration of usual features: try to right click on a file on a MTP drive, you don't have the usual UI things like Open with etc.)
FTP server solutions (good solution, but 1) how to use this if I'm on the road, with no Wifi router like at home? then I cannot link
computer <---> phone? 2) it seems that such an app doesn't offer access to external sd card)
But with all these methods, you don't really have access on your computer to the phone's filesystem like if it was a local folder.
Isn't there no solution in 2017 that makes it possible to browse the phone's filesystem as if it was a computer local folder, easily?