When comparing Dolphin vs Nemo, the Slant community recommends Dolphin for most people. In the question“What are the best file managers for UNIX-like systems?” Dolphin is ranked 3rd while Nemo is ranked 7th. The most important reason people chose Dolphin is:
As with any KDE app, Dolphin, allows adding or modifying toolbar buttons and keyboard shortcuts.
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Pros
Pro Immenseley configurable
As with any KDE app, Dolphin, allows adding or modifying toolbar buttons and keyboard shortcuts.
Pro Can split views
Dolphin supports splitting the view in two navigational areas, this way you can navigate two different directories at the same time.
Pro Integrated terminal
Pressing F4 with any opened folder on a mounted path opens a console within dolphin.
Pro Also has a refresh option
Dolphin is without a doubt the best fully functional and easy to use and multitask with.
Dolphin also has a refresh button which no other File manager has. It's great for tracking a large files transfer; that's what file managers are for - good common sense.
Pro Easy to extend with plugins
Dolphin follows KDE's philosophy of being extendable and configurable. It can easily be configured and customized through plugins.
Pro Auto mounts flash drives
Dolphin automatically identifies and mounts external flash drives.
Pro Fast at opening graphics folders
Pictures with or without previews is optional and selectable at the touch of a button.
Pro Does not use third party libraries
Unlike all those GTK-based file managers it does not have to rely on external written software for its functionality because KF5 is KDE SOftware and developed alongside.
Pro Keeps its state
It starts with last opened folders.
Pro Fully supports HiDPI
Supports HiDPI displays.
Pro Automatically centers items
In icons view mode, the space between files gets stretched so that there is never and annoying empty space at the right side of the window.
Pro Elegant
The most stylish among all FMs.
Pro Extendable
Nemo can be extended to have additional features through third party plugins.
Pro Easily open as root
Option to open folder as root from within the right click menu.
Pro Easily open file location in terminal
Option to open a folder in terminal, which can help executing commands such as bash.
Pro Has dual pane functionality
This functionality was removed in Nautilus and Dolphin at least in Ubuntu-Gnome, but Nemo kept this option, making the obvious functionality of cut, copy and paste much easier.
Pro Double pane and search by name capabilities
Pro Supports bookmarking
You can bookmark folders that you open often, this way you can easily access them from anywhere while using Nemo.
Pro Good networking options
Supports ftp, ssh and samba connections.
Pro Queues file operations
Cons
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.
Con Can hang on remote file systems
It doesn't cope well with remote file system nicely like sshfs or any samba, like when network is not responding/very slow. It just hangs.
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.
Con Poor optimization on later versions
Con Too simple
Feels weird on KDE because it has less customizing options Konqueror and any other KDE app have.
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.
Con Changing the background color or font type for customization is not practical
You have to do it with finding and editing the relevant CSS files. No buttons, menus or sliders for such customization.
Con Incomplete mimetypes
Like all nautilus forks it allows you to run svg-files due some incomplete mimetype coverage.
Con Depends on GNOME
Depends on gnome toolkits an libraries.