When comparing RCDefaultApp vs ImageOptim, the Slant community recommends ImageOptim for most people. In the question“What are the best power user tools for macOS?” ImageOptim is ranked 8th while RCDefaultApp is ranked 69th. The most important reason people chose ImageOptim is:
Great for compressing images for web usage or saving harddrive space.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Provides missing functionality
Standard features on Windows, but not on Mac, this fixes that.
Pro Losslessly compresses PNG, GIF, and JPEG images
Great for compressing images for web usage or saving harddrive space.
Pro Fast & Simple
Pro Simple drag'n' drop interface
Simply drag images (or folders) into the window.
Pro Tries several different image optimizers before picking the best one
Pro Edits files in place
It does edit files in place, overwriting the original. This is exactly what I want, so I love it, but it's good to know beforehand.
Pro Can handle PNG, GIF, and JPEG images
Great for compressing images for web usage or saving harddrive space.
Cons
Con Last update was in 2009
But the software still works, so far no issues on El Capitan 10.11.3.
Con Compression algorithm not as good as counterparts
Con Cannot abort an optimization
Optimization can run for a long time. Sometimes it reaches 20% quickly and then spend a long time to attain 21.2%. But you cannot interrupt the process.