My buddy has one of those Ryobi saws. It's ok for that one time you need a cordless saw, but for general use it's really a pain. The batteries they ship with their stock kit, it'll last through maybe a half dozen 2x4s and then just die. I was looking at the Milwaukee cordless kit, and they won't even let you use the saw without the extended capacity battery.
I have a Makita 5007NB corded circular saw I bought maybe 15 years ago.
My experience... the hard case is especially important with a circular saw. I used to just toss mine in any old box, and it seemed ok until I started having binding problems while cutting and it was a pain adjusting the height and it took me a while of fighting with the saw to realize the reason why was because the base plate had bent. Or rather the bracket which mounts to the base plate and allows for height adjustment had bent and shifted the base plate so it wasn't quite flat from front to rear.
A replacement base plate was about $20, and after replacing it I've taken better care of the saw and kept it in the case when not in use.
I still just toss my cordless drill in a tool bag, even though that also came with a case.