When comparing feh vs GPicView, the Slant community recommends feh for most people. In the question“What are the best FOSS image viewers for UNIX-like systems?” feh is ranked 3rd while GPicView is ranked 13th.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Loads up images extremely fast
Pro Minimalistic
Goes well with tiling window managers.
Pro Multiple windows
When opening multiple images at once it opens every single picture in a separate window.
Pro Functional
It has all the necessary functions that you can reasonably expect from a lightweight image viewer: you can view all the image files in a directory, rotate and save them.
Pro Customizable
Pro Extremely lightweight
And still you can browse all images in a directory.
Cons
Con Junky rescaling by default in WMs
Fixable by running these commands:
echo "alias feh='feh --scale-down --image-bg black & disown" >> ~/.bashrc
source ~/.bash_profile
But after entering those two commands for all users, feh works flawlessly, and is extremely responsive. Would definitely recommend.