What is TGZ?

A tar bundle compressed with gzip - the standard Unix archive. Because gzip sees the whole bundle at once rather than each file separately, a folder of similar files compresses better than the ZIP equivalent. The catch is that reaching one file means decompressing everything before it.

What is ZIP?

The archive format both Windows and macOS open by double-clicking, which is most of why it won. Each file inside is compressed on its own, so you can pull one out without unpacking the rest - handy for browsing, slightly worse for compression ratio.