A circular saw is used primarily to cut sheet material like the sheathing. A good circular saw finds a balance between power and weight. My personal circular saw is an older 15-amp Milwaukee that is a beast, but it weighs about 12 pounds. After just a few cuts I really start to feel it in my arm. This can be exacerbated by any attachments like the Kreg Rip-Cut that I talk about in the table saw section.
Our team tested 4 circular saws and found the best to be the DEWALT DWE575SB 7-1/4-Inch Lightweight Circular Saw with Electric Brake . It is compact, powerful, and relatively lightweight. The trifecta of a perfect power tool. Another feature that we liked is the electric brake. This stopped the blade from spinning much faster than the saws without this feature, and the faster the blade stops, the smaller the window for an accident. We also liked the ability to achieve greater bevel angles with the DeWalt, and the guard design is one of the best we’ve seen as it rarely got caught on the lumber.