My Cochins have been super strong and healthy. LF and bantam. Only if I bring in a few certain bloodlines have I lost any and I fear it is from them being kept in more "secure" conditions than I have ever allowed mine. I treat all of mine like chickens and they get dirt clods from my barnyard from 2 weeks old and up along with some grass attached.
My Marans can be strong but so far only one bloodline has been doing well for me. I have brought in a few other bloodlines that I am watching as they mature with some being hardy and others not making it past 2 months old. I figure I will stick with the Whitmore Farms birds since they have been great for me for several years.
My cuckoo Marans from hatcheries are mostly okay. I have other problems with them like crop problems that cause them to have to be culled.
I got some d'Uccle hatching eggs from 4 different breeders this year. My first year with d'Uccles and one breeders' birds all have lived while 2 of them didn't make it out of the brooder and one has faltered a bit.
My Araucanas have always been strong. None have ever gotten sick.
Certain Ameraucana bloodlines have been good while Easter Eggers from hatcheries were always hardy for me.
My Silkies have been okay. The ones I first got years ago from Fluff N Stuff Silkies are still around and have seen sick birds come and go but they have not ever gotten sick. Some other Silkies I have gotten from others have done well but I have hatched from some breeders and the chicks never make it out of the brooder or if they do then they do not live long.
My Wyandottes have been okay. The BLRW I raised this year from the Foley bloodline have done extremely well, while some SLW chicks have made it out of the brooder room from other breeders. My own SLW chicks I hatched and raised from my collection of birds have done well even mixed in with those that didn't.
I do tag my chicks to keep up with bloodlines.
I got some Partridge Rocks years ago and those girls are still here and kicking well from Meyer hatchery. I got more this year and all those are 4 months old now and have been fine.
I have many breeds in my free range flock and I try to keep going with the ones that do well for me. The Jersey Giants have been great but the Langshans breed I have ordered twice from 2 separate hatcheries and only have one pullet to show for it. I have a Langshans roo that was given to me several years ago that came to me sick, mostly just covered up in internal and external parasites. Once cleared up he has been great and his daughters out of the Jersey Giant hens have been really good and strong.
Delawares were a bust for me, from breeders and hatcheries. Brahmas have been good for me except for the light ones I hatched from a breeder. I have 2 left and they are not thrifty. They eat well and play but are not as big as the dark Brahmas I hatched at the same time nor as good as the ones I got from a hatchery. But I did lose some dark Brahmas I got from the hatchery.
Red sex links have always done well for me. I like to keep those in my free range flock.
Hatchery stock buff Orps have been good.
I am sure there are a few others but that is the list I can think of now.