I have free ranged all groups here for the past 9 years. No predator losses. I do have roosters with them, however, so always an alert system in place and each group has always had a pen attached to the coop for when we are not home. We DO NOT free range any flocks when we are not home. That's pretty much asking for trouble up here in the mountains.
My flocks consist of Plymouth Rocks, Delawares, crosses of those two, plus some miscellaneous Easter Eggers, a couple of true Ameraucanas and some other mixed breeds. I have one 8 yr old Brahma hen, used to have a Lt Brahma who passed away almost 3 yrs ago and those two are good free rangers, seemingly impervious to heat or cold. The Delawares are first to pant in hot, humid weather, probably due to their dense musculature and tight feathering.
I also have Belgian D'Anvers, a very small bantam that is under covered pen 24/7 except on rare occasion when I let the group out to free range under VERY close supervision-surprisingly, they are avid foragers, but I can't leave them out due to their small size and living on a mountain property with every predator you can imagine here. They love, love, LOVE to dig around this place, though, and being a mille fleur pattern, most of them anyway, they are very camouflaged in the oak leaves.
My Rocks, both blue/black/splash and barred varieties are avid foragers, as well as my Delawares. My crosses, which include the Easter Eggers are great at free ranging as well. The ones I see least likely to forage, but want to find the humans to hold them and baby them are my true Ameraucana hens-those tend to do a little digging, but stop and look for me or just go back to the coop.
Used to have RIRs as well as Wyandottes, both good free rangers, especially the big, dark heritage RIR hens. Busy, quiet, minded their business.
In November, a stray tomcat adopted us and we had him neutered when it appeared he was staying put. He doesn't hurt the birds, usually avoids them, though he likes to play "chicken bowling" just to see them run and squawk. He doesn't actually make contact with any of them. The roosters keep an eye on his antics. Over the years, cats have come and gone (not mine, strays), but none have hurt any chickens, though I'd never trust a cat around chicks.
ETA: I realize that we have beaten the odds with no predator losses for 9 years, however, eventually, our number will come up. It's inevitable with free ranging and no livestock guardian dog.