What's in a breed? Lots, as it turns out. Different chicken breeds have different temperaments, different appearances and different maintenance requirements that come along with that.
There are all different varieties of chickens out there and it's so, so hard not to want them all! I myself want so many that I have a pretty extensive wish list I have compiled and sometimes I just like to look at it and maybe rearrange the order a little here and there...you get the idea.
For anyone interested there is a great chart in Storey's Guide to Raising Chickens by Gail Damerow on page 8 that lists breeds and some of their main characteristics. The information is general to the breeds, and not every bird will fit in the descriptions. We have had a few Buff Orpingtons that have not been incredibly friendly, and I know some people swear by the sweetness of their Rhode Island Reds, which have a sometimes aggressive notation. Individual personalities come with the territory I guess.
In choosing breeds sometimes just trying to match your climate and purpose is a good place to start, are you in a hot place like I am (Phoenix, AZ), or a cold place? I approached it with thought to my extremes. We get incredibly hot here and I was very worried about our girls dying from overheating. I avoided ordering any girls that were noted as not heat tolerant at the hatcheries. I looked at heat tolerant birds and was pleasantly surprised with the variety that was available. Maybe some day I'll live up north and finally check that Salmon Faverolle off my chicken bucket list. In terms of purpose, how important are eggs, and do you want them year round? Some breeds are stellar egg layers, some...not so much. Our Easter Eggers and Delaware are pretty good at laying occasionally through the winter with the eggception being their molt. Our Polish ladies are known for taking long (read: 2-3 month) breaks and so we don't see eggs from late fall to late spring. They are pretty girls that rely on their looks and sweet personalities to pay the bills for them. Broodiness is another thing to think about. Are you planning on hatching chicks? A broody hen can do all that scary work for you and prevent you from a lot of sleepless hours staring into an incubator and playing hours long loops of cheeping baby chicks to your hatching eggs at midnight the last three days of incubation (a scenario mostly based on real life). The flip side of a broody hen is that she won't lay, becomes super cranky and if you can't have a rooster then it becomes a bit of a problem to manage. It's never completely foolproof to plan to have a broody or non-broody hen, but buying breeds that are known to be less broody is a good start.
Egg color! Before backyard chickens I had no idea there were blue eggs. Or green eggs. Or olive eggs. Or deep, dark, rich brown eggs. I thought there were white eggs and light brown eggs, full stop. From the baby blue of our Super blue layer from My Pet Chicken, to our dark brown and sometimes spotted egg of our Delaware, it's been fun to collect the beautiful rainbow of eggs that our girls lay. I'd say it's very fair to plan a flock around what eggs you want and since there is so much variety it becomes so fun! In the past few years there have been specialty breeds popping up, bred for specific colors of green or blue or brown, which is a fun thing to explore.
Appearance. I'm so into my Polish girls. Crested chickens are my kryptonite, apparently. I also love the fluffy muffs and beards of my EE's. The beautiful fluffy skirts that Orpingtons and other dual purpose chickens sport make me laugh when they run like English ladies with their fluffy petticoats. I tend to choose chickens by how they look as well as how they might act or lay. It's a delight to watch my big booty girls run to me, bouncing side to side and so exuberant, though the sleek stride of my slender EE's gives me a sense of delight, as I can see a dinosaur running at me every day. My Speckled Sussex is just the most glorious thing in the light, she's a party for your retinas.
Health. While I almost didn't include this, one of the big lessons I learned is that sometimes chickens come with their own sets of health issues. An obvious example is Cornish cross AKA "meat birds". Cornish Cross are meant to be harvested in 6-8 weeks. Yeah. Weeks. They get huge, they eat a ton and it becomes physically challenging to do things like stand, walk, exist. It wouldn't be a good breed to try to make a pet out of, though some do and put them on diets and they live long and happy lives. Going in not a lot of people might be up to that challenge though, so it's worth noting. Another thing we learned from experience is that there are lines of hatchery Buff Orpingtons that are much more prone to dying of a liver bleed (Hemorrhagic liver disease) if over fed or given too many snacks. We have actually not had any Orpington make it past 3 years old. It's heartbreaking because they are in general very nice birds. Our last remaining BO has severe problems with her reproductive tract, I am guessing another couple years and she will have problems we can't fix. She is currently our last and longest lived Orpington at just over 2 years. Our Easter Egger is our OG girl and is a ripe old 5 year old bird who rules with an iron beak. We have never lost an EE, maybe mutts really are more hardy!
Choosing breeds is one of the first steps of a new chicken owner and when confronted with all the choices (was) can be overwhelming. I remember in the beginning really feeling overwhelmed and worried I would choose a breed that I was condemning to death in our very hot summers. Our first flock's purpose was as pets for us and children too, so was I going to choose a breed that I found out later was aggressive toward people? There are a lot of types of chickens to choose from and weeding out what you "can't" have first sometimes helps. Once you narrow down your A team, so to speak, you can start adding to your wish list.