This is JMHO and a little sad experience. Friend and I had Marans and found them aggressive birds toward smaller or docile breeds (like Silkies, Ameraucanas, and EEs) and we re-homed all our Marans (Cuckoos and BCMs). We got about 3 eggs/week from them but they were never "chocolate" and seems only a few lucky owners or breeders get the really dark dark eggs. A friend's first Welsummer egg was darker than our Cuckoo's or our friend's BCM eggs. Our friend found their BCMs became very combative as adults toward other heritage/dual purpose flockmates. This is what a little Silkie looked like after our Cuckoo Marans chewed on her and outright viciously attacked another Silkie pullet. I thought the Silkie was molting but it was the Marans eating her alive!
Leghorns of all varieties are classified under the Mediterranean class and although lighterweight birds, they have a tendency to get aggressive to downright cannibalistic in a mixed flock. My folks raised Babcock Leghorns (white) and they were fine within their own breed flock or other Mediterranean class breeds but Legs around gentle or timid birds like EEs will eventually stress the jittery jumpy timid EEs. Our Buff Leghorn started to yank out all the crests, muffs, and beards of our gentle Silkies and Ameraucana so we had to re-home her. Our White Leghorn went bonkers out of nowhere on her flockmates after her 3rd year in the flock. The only good Leg layers are the White with Brown coming in second - all other varieties are not as good, including the Exchequer. Other Leg owners have said they think Legs are positively crazy but I say they just shouldn't be mixed with timid or docile breeds.
I've talked with people who have CLs and think they are great birds except some have said they weren't very good layers but that is just input I got from owners and haven't raised CLs myself. I personally am going to avoid blue-egg gene breeds in the future as I am finding not very promising production in them - Ameraucana, Araucana, CLs, EEs, Isbar, and Olive Eggers. My egg-seller friend has re-homed all her Amer, EEs, and OEs for low production and a Farmers' Market egg-seller says they won't get any more EE because of poor or sporadic laying.
People I contacted in the past that had Marraduna Basque for sale suddenly are no longer breeding them and I don't understand why since they caused such an interest when first introduced.
Currently the big craze seems to be the Bielefelders that are reportedly gentle giants and eventually lay jumbo to double yolker brown eggs. The BYC Bielie thread is a very fast growing thread with delighted people discovering this new breed. Being a fluffier-feathered breed they probably take the colder climates well. If I didn't have Silkie bantams in my flock I would've liked to try a gentle giant Bielie just to see what all the hype was about. I was always intrigued by the genlte giant Brahmas but apparently the big Bielies are better as jumbo egg layers.
Whatever breeds you decide on I wish you well. I've had 5 years of trial and error and decided I preferred a peaceful flock over having a colorful egg basket. My gentles flock consists of Silkies, Ameraucana, and Breda. My Amer is a dud layer her 2nd year giving us only 3 eggs. She is jittery and jumpy and runs from all the other hens rather than engaging in flock politics. She comes up to me and let's me pet and hold her but as soon as another chicken approaches she bolts. I might re-home her into a friend's EE flock to see if she gets along better with her own breed type. I get nervous watching her be nervous LOL!
