Compared to xz and even parallel xz, gzip and parallel gzip are just better if speed is more important. The compression is not superior but already good if you consider just the uncompressed data. For long term storage, it makes sense, to invest the extra time for better compression but if it's about transfer time, you might end up with a overall longer processing time instead of just a longer transfer time because of a worse compression ratio. It's like with image formats: Pick the right one for your use case.