Why not dual purpose?
They are naturally healthier than broilers. They can breed normally, so you can hatch your own chicks without having to order batches of chicks all the time (saving money?). Many of the "heritage breed" hens will even hatch eggs for you and take care of the chicks (again, saving money?).
You can have eggs to eat, and you can slaughter for meat your surplus young males and your hens that are too old to lay and your roosters that are too old to be fertile anymore, as well as any other culls (chickens you don't want to keep around for whatever reason). Since dual-purpose mature at a balanced rate, they don't all have to be slaughtered within a narrow window of time like broilers--you can slaughter young cockerels (or pullets, if you have too many) anywhere from 3 1/2 months to 7 months, depending on whether you want "game hens" or "slow roasters" or anything in between, and old hens or roosters past their prime can be slaughtered whenever, as needed, for soup or stew or braising.
Because of their balanced growth, they also suffer less health problems, don't require such demanding and precise food rations, and yield more nutritious and more flavorful meat.
Also, there are many beautiful and historical breeds to choose from that are all very useful in these regards, many of which are well adapted to particular climates or conditions or specific needs, and many have wonderful and colorful histories to boot. Some of them are in danger of extinction, and could use more support and interest from home flock owners.
There's more to "efficiency" and usefulness to consider than just "feed conversion" and "yield." We don't need to be perpetuating the factory farm propaganda...
Good luck, whatever you choose!