Honestly, depends on your use-case. Spacebadgers generates minified and brotli-compressed SVG code instead of images, so we can run on the edge with very little performance overhead. Due to the reduced bandwidth, we can also serve badges with much shorter cache-times, so they update more frequently. I suppose if you're happy with shields.io, there's no good reason to switch, but for people who are actively looking for a faster alternative, or want to get some fresh badges for a new project, Spacebadgers is a great alternative.