BlackBox focuses on extreme compression for low-end PCs. Their version is smaller (roughly 1.8GB), but it often removes the in-game radio stations to save space. If you just want the core story and don't care about listening to the in-game soundtrack, this is the most compact option.
Highly compressed versions of Saints Row: The Third run to the original retail version after installation. Compression only affects the download and setup process, not runtime. You will still get: best download saints row the third pc highly compressed