Chicks are generally ordered from a hatchery. If you order them from your local feed store they are more than likely getting them from a hatchery. Hatcheries, unless they are specialized, carry only a couple of varieties of broilers (meat birds). They carry breeds that perform well and convert feed efficiently - which are generally not breeds that are endangered, or heirloom or interesting. It turns out that there are basically 2 options: quick growing and slow growing.
The quick growing birds are what I would consider "commercial" birds. They reach their optimum slaughter weight at 9 weeks. The breed (if you could call it that) has been developed to be incredibly efficient at converting feed into body weight. Apparently, they are content to sit at their feeders all day eating and putting on weight. They grow so fast that they are prone to heart attacks and leg problems. It is recommended that they be slaughtered no later than 9 weeks or they start dying from heart and lung problems.
Then there are the slow-growers. These are also hybrid birds, but ones that grow at a more traditional rate. This breed takes 14 or so weeks to reach market weight.
It is also possible to get more dual-purpose birds to raise as meat birds - these would be breeds that both lay eggs but also put on weight (such as Plymouth Bar Rocks). But efficiency is something that can't be underestimated when you are raising meat birds. You need to balance ideals with economics. If the birds take too long to reach a suitable weight (ie a weight that your customers will want), then you are feeding them to some extent. The cost of feeding them depends on how much of their diet is supplemented by either foraging on pasture or supplied (eg. kitchen scraps). But the cost of feeding has to be taken into consideration when you calculate the price per pound that you'll sell the meat for. So, while the more traditional dual-purpose breeds seemed less engineered, I ended up going with the slow-growth broilers. Michele, who has more experience than me, was very convincing about the feed expense.
We ended up ordering 60 slow-growth broilers. 20 for each family, and then 20 for our egg customers. They are slated to arrive May 7.