When comparing Irfanview vs ShareX, the Slant community recommends ShareX for most people. In the question“What are the best screen capture tools for Windows?” ShareX is ranked 1st while Irfanview is ranked 13th. The most important reason people chose ShareX is:
Designed as file uploader in the first place, ShareX supports overhelming amount of services for you to upload your files to and the list is expanding.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Some editing tools included (cropping, color correcting, etc...)
Pro Lots of plugins available
Plugins can be found here.
Pro Batch processing
Even exif information can be batch processed.
Pro Recognizes virtually any image format
Pro You can just scroll with your mouse to explore images
Pro Ultra fast
If you press and hold the right-arrow button (for displaying the next image), you can watch images pass by as if they are a video, it's that fast. No stuttering, it loads images as fast as your hard drive can keep up.
Pro Lightweight
Pro Can use 8bf (Photoshop) filters
Pro Easy updates
Very easy to update the program and its associated plugins.
Pro Irfanview Thumbnail Viewer is a convenient way to view all image files easily
Irfanview Thumbnail Viewer is a great way to view thumbnails of all image files, including thumbnails of WMF files which Windows cannot natively display.
Pro Allows uploading to a vast number of different services
Designed as file uploader in the first place, ShareX supports overhelming amount of services for you to upload your files to and the list is expanding.
Pro Free and open source
ShareX is licensed under GPL with source code available on GitHub.
Pro Customizable
You can choose what shortcut key to bind your command to, as well what host it uploads the file to.
Pro Freezes screen when you capture
When you enter a capture mode, the screen content is preserved as it was when you started capturing by default. However there is a special "Light" mode where the screen does not freeze.
Pro Can capture video too
Apart from still images, ShareX allows the user to record unlimited video with all the options available for normal image capture.
Pro Capturing (screen, video, a window, etc.) with annotation + automation
Capturing (screen, video, a window, etc.) with annotation + automation makes for some powerful workflows.
Annotation is key for research on any project size. Capturing screenshots, editing them ("annotating"), converting to a PNG, removing the background to make a transparent version, saving to google drive, creating large+med+sm sizes, uploading thumbnails, is an example of a workflow you could create. The list goes on...
You'll find the same strength & depth in features for image handling also for text, videos, other files by type, and on and on..
Pro Has an editor
It has its own screen editing tool.
Pro It has a dead simple way for creating animated GIFs
It is great for creating software tutorials or highlighting new features in a sales function - nothing beats a well-placed animated GIF in an email.
Cons
Con GIF viewing is buggy
GIF viewing has longstanding problems like flickering, incorrect framerate or artifacts, and it is very unlikely that it will be ever fixed.
Con Irfanview Thumbnail Viewer crashes on accessing AVI files
For some reason, the Irfanview Thumbnail Viewer crashes when it tries to access any .AVI movie file.
Con No transparency support
The alpha is converted to the selected background color upon opening a picture. When saving the picture again, you can select a color which is converted to alpha again.
Con Missing some utilities
Like browsing files utility.
Con Preferences are hard to find
Con Windows only
Con UI is far from ideal
Sometimes the interface is confusing.
Con Too complicated
This is extremely customizable, but extremely complex! If you want something simple and intuitive out of the box, stay away from ShareX.
Con Privacy concern
Can upload screenshots to web without you realizing, unable to delete or reverse process.
Con Scrolling window capture doesn't work always as expected
Sometimes might need to use another screen capture software to capture a scrolling page.
Con The editor is rather simplistic
