ImageMagick has more features but SIPS covers almost all of the ones I’ve ever needed to use, and it’s much faster (sometimes an order of magnitude or more, see below) and tends to be better at correctness around colorspaces and formats.
I noticed this most noticeably working with JPEG-2000 files (I work at a library with large collections of scanned images). ImageMagick technically supported the format but it was by the Jasper library which was extremely slow and, worse, had a fair number of images which it couldn’t decode correctly so you’d get a black box from an allegedly error-free pass.
I never hit an issue with CoreImage like that, which was a point in favor of trustworthiness. The performance benefits varied but I never found a case where ImageMagick was faster or even less than a whole multiple slower.
I noticed this most noticeably working with JPEG-2000 files (I work at a library with large collections of scanned images). ImageMagick technically supported the format but it was by the Jasper library which was extremely slow and, worse, had a fair number of images which it couldn’t decode correctly so you’d get a black box from an allegedly error-free pass.
I never hit an issue with CoreImage like that, which was a point in favor of trustworthiness. The performance benefits varied but I never found a case where ImageMagick was faster or even less than a whole multiple slower.