My 2 favorite sets of chickens so far are complete mutts. I had standards that were half welsummer and then pendesenca x maran in an unknown amount. They were huge, they laid big chocolate eggs with black spots, good layers, very good free rangers, and they handled our weather extremes with only some minor comb frostbite. I butchered many for meat. Their only down side was that they were very slow to mature. They didn't lay until about 8months and I could hardly tell the breeds apart until 6months. Wasn't really an issue with 170sq ft of coop space and 40 acres of land. They mostly fed themselves aside from winter. I went several months in late summer and fall without buying a bag of feed for them. Then they were my bantam EE which I know had some d'uccle blood in them and the rest is a mystery. Very good layers, wonderful broody, hardy, perfect sky blue eggs, and I had several 100% hatches from them.
I will probably never see birds like that again. Luckily there are tons of breeds and even more crosses I can play with whenever I get in to chickens again.