When comparing ImageOptim vs Notational Velocity, 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 Notational Velocity is ranked 11th. 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 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.
Pro Simple and minimalistic
The interface is clean and unobtrusive.
Pro Free
Pro Syncs with SimpleNotes or Dropbox
Cons
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.
Con Does not work on SVG yet
Con Feels a bit outdated
The last release was from 2011. Although due to its brilliant simplicity in doing what it's designed for, some might think there hasn't been any need for an update, as long as it still works with the newer OSs.