Recs.
Updated
Dolphin is a lightweight file manager. It has been designed with ease of use and simplicity in mind, while still allowing flexibility and customisation.
Specs
Pros
Pro Supports different protocols through KIO (sftp, fish, ssh etc...)
Like other KDE applications, Dolphin makes use of KIO which gives Dolphin access to other APIs and services. For example, it allows Dolphin to manage files stored remotely the same way you can manage local files through FTP.
Pro Fast and intuitive
Minimal startup delay, and rapidly accomplishes sorting, searching, and moving of files regardless of file type. On statistical average Dolphin was 20% faster than Nautilus or Midnight Commander (based upon groups of 500 files of 5 MB to 10 MB each in over a series 1000 timed runs).
Cons
Con Heavy and DE specific
Unless you are a KDE user, Dolphin requires a lot of files/libraries and about 130+ MB of disk space. That's 85% larger than Nautilus on a (non-GNOME) installation and closer to 95% larger than PCManFM.
UPDATE:
In both cases mentioned Dolphin also has an equally increased functionality, system integration, and customization options. When all three FMs are on the same "independent" (i.e. not native to, or forks of, any of the three FM's originating) desktops running with equal functionality they are within 15% of the same size. Given the normal variance caused by choice of programing languages and algorithms, they are statistically identical.
Con Can't search contents of hidden folders
When "Hidden Files" is enabled, searching (Ctrl+F) does not search hidden files and folders. Numerous bug reports have been filed against this, but the developers are too short-sighted, marking these bugs as "Resolved Intentional".
Although hidden files / folders should not be searched when that flag is not enabled, they most definitely should when that flag is enabled.
UPDATE:
The "Show Hidden Files" switch only changes the on screen visibility of files. It has no effect on the files themselves, nor does it enable any functionality that was no already present.
While they may visually appear related, searching is a completely separate function from viewing So much so that there exists a complete science developed just to search algorithms. To date, viewing a list of contents has no such comparative science or rigor. I
n all Linux and Unix distributions, hidden files have always begun with "." as the initial character. This has been true in the 1970s. As such, anyone working on an "*nix" that is looking at hidden files would reasonably be expected o know this. Thus for system stability and safety, a search of hidden files requires the use of "." followed by the search string and/or wild cards (again something well know by persons will sufficient knowledge to safely navigate hidden files.)
Con Too simple
Feels weird on KDE because it has less customizing options than Konqueror and any other KDE app have.
Con "Type" column too verbose
Despite having a large enough monitor, If you keep the size of the browser window small, the "Type" column (in "Details" view mode) insists on including the complete multipart MIME string, making the column so wide that trying to limit its width makes the column useless. Sorting by "Type" renders the list into an incomprehensible mess.
UPDATE:
When sorting by Type, Dolphin simply organizes the already established list by grouping according to the characters following the right most "." in the file name. If your list was alphanumeric previously, then it will be alphanumeric within each of the groups - exactly as you told it to do. This is by totally comprehensible if you are looking for a file and know that it is a particular Type, say for example a PDF. My own library has over 2200 reference books and papers and over 3600 works of fiction, comprised of some 17 different file types. Sorting the alphanumeric list by Type makes short work of find the PDF Textbooks, abstracts, and thesis from over 250GB of literature.
Con Slow on startup
Dolphin can be a little slow on startup (depending on distro, hardware, etc.). Startup time can vary from a couple of seconds to up to a minute.
Con Looks too ugly in Gnome (Windows 1998 look)
If you use Arc, Adapta, Breeze or Adwaita theme engine it can look consistent with GNOME applications with Kvantum.
Con Searching files is horrible until indexing is disabled in plasma settings. Even then, it is not great.
Con Unclear how to request a hash check for file copy or move operation like MidNight Commander
Recommendations
Comments
Flagged Pros + Cons
Pro Integrated terminal
Pressing F4 with any opened folder on a mounted path opens a console within dolphin.
Con May be a little slow on startup
Dolphin can be a little slow on startup (depending on distro, hardware etc...). Startup time can vary from a couple of seconds to up to a minute.
Out of Date Pros + Cons
Con Can't perform ROOT actions
Developers set a constraint in Dolphin that deny Dolphin to run with root permissions. Hence, if you want to perform an action that require root permissions, such as rename a file in /etc/ folder, you are forced to use terminal or switch to another file manager.
UPDATE:
This has been false since 2014. Right click allows the choice to open any file in supper user mode (SU) in a second window. It is still the same file manager however you are now using it as root. Files can readily be transferred between windows, renamed, re-permissioned, deleted etc. This functionality remains so long as the SU is open. The SU window has full and unrestricted access to all files regardless of the location you entered SU.