What is the most efficient yet versatile image viewer?

[joe at actionline.com]

What is the most efficient yet versatile (multi-functional) image viewer?

For many years, I used 'kview' and 'kuickshow' but I cannot find either in
any current *buntu repository. Rather, it seems that many Linux
application developers are prone to make things more and more complex and
less efficient and streamlined.

I have found 'feh' to be one very good option. (What does 'f.e.h.' stand
for anyway?)

However, as far as I know, 'feh' does not include any editing options to
resize, crop, etc. or to slide-show view multiple images.

Gwenview seems to be the current default viewer (who is 'Gwen'?) and it
has many nice features, but it seems rather cluttered up with too much
'stuff' in the window when it is opened. And, every time I type 'gwenview'
on the command line, the terminal displays a long list of error messages
(see below) that I don't know how to stop from displaying.

$ gwenview
"/usr/bin/gwenview(27474)" Soprano:
"org.freedesktop.DBus.Error.ServiceUnknown - The name
org.kde.nepomuk.services.nepomukstorage was not provided by any .service
files"
"/usr/bin/gwenview(27474)" Soprano: "QLocalSocket::connectToServer:
Invalid name"
"/usr/bin/gwenview(27474)" Soprano:
"org.freedesktop.DBus.Error.ServiceUnknown - The name
org.kde.nepomuk.services.nepomukstorage was not provided by any .service
files"
"/usr/bin/gwenview(27474)" Soprano: "QLocalSocket::connectToServer:
Invalid name"
"/usr/bin/gwenview(27474)" Soprano:
"org.freedesktop.DBus.Error.ServiceUnknown - The name
org.kde.nepomuk.services.nepomukstorage was not provided by any .service
files"
"/usr/bin/gwenview(27474)" Soprano: "QLocalSocket::connectToServer:
Invalid name"
"/usr/bin/gwenview(27474)" Soprano:
"org.freedesktop.DBus.Error.ServiceUnknown - The name
org.kde.nepomuk.services.nepomukstorage was not provided by any .service
files"
"/usr/bin/gwenview(27474)" Soprano: "QLocalSocket::connectToServer:
Invalid name"
QInotifyFileSystemWatcherEngine::addPaths: inotify_add_watch failed: No
such file or directory
QFileSystemWatcher: failed to add paths: /home/joe/.config/ibus/bus
"/usr/bin/gwenview(27474)" Soprano:
"org.freedesktop.DBus.Error.ServiceUnknown - The name
org.kde.nepomuk.services.nepomukstorage was not provided by any .service
files"
"/usr/bin/gwenview(27474)" Soprano: "QLocalSocket::connectToServer:
Invalid name"
gwenview(27474)/kdeui (kdelibs): Attempt to use QAction "edit_redo" with
KXMLGUIFactory!
gwenview(27474)/kdeui (kdelibs): Attempt to use QAction "edit_undo" with
KXMLGUIFactory!
"/usr/bin/gwenview(27474)" Soprano:
"org.freedesktop.DBus.Error.ServiceUnknown - The name
org.kde.nepomuk.services.nepomukstorage was not provided by any .service
files"
"/usr/bin/gwenview(27474)" Soprano: "QLocalSocket::connectToServer:
Invalid name"