I've teetered between MATE and KDE for the last couple of years -- they're both great, but I like KDE's interface and look/feel a bit more. Also, Dolphin is, IMHO the best file manager for Linux.
But, the thing that still pisses me off about KDE is the handling of cifs mounting (a la smb://). In MATE (or Cinnamon or Gnome2), if I mount a share with smb:// in the file manager (Nautilus, or the newer ones), I get an actual cifs mount. Now, if I open a file on that mount with a photo viewer, or a media player (like VLC), the file manager throws a locally-mounted and accessible file path to the application.
Not so with KDE. Doing the same thing from Dolphin throws the URL of the file (smb://server/share/file.ext) to the application, and the application usually has no effing idea what to do with this. So, I end up either copying the file to my local hdd and opening it from there, or adding an entry to fstab to get a real mount (which is not practical if mounting a new share on someone else's server.)
The gvfs way is better than the KIO way.