Best Stuffpack for CAS?

Depends on what you want. :p I got Backyard stuff because I like the summer clothing, especially the muscle tank (since the base game lacks options for tank tops). I also got Laundry Day because I like the boho aesthetic. The boots, the dress, the men's shirts and sweater--those were all things I could use.

I suggest going to the game's main menu, clicking on each SP icon to preview the CAS items, and go from there. :)