For fast meat go straight to the Cornish Cross (CX). Not the tastiest or firmest, but quick, cheap and better than grocery stores. 8 weeks to butcher.
For Dual Purpose (DP), hatchery stock tends to be smaller and geared to egg laying, but they eat just fine. Expect 16 or more week grow outs and less meat per bird. Better taste, firmer flesh and will forage given enough room.
Meat birds other than CX that includes Freedom Rangers, Dixie Rangers, Imperial Broilers and all the other broilers can be explained by saying slower growing (12-24 weeks to butcher) birds that can get as large as the CX.
I started with CX. All the bad things you hear are not due to the breed, but the care they receive. They will outgrow their bodies and hang around the feeders unless you make them forage. The couch potatoes of the chicken world.
Research. See what everyone says here. Then figure out how much time, money and effort you have or want to invest in good food.
For butchering, take your time. Adding stress to your life will sour the experience for all involved. 20 birds is a good number. Enough to keep you from making pets and few enough to handle easily. I'll butcher 2-7 a day depending on how I feel. If you have helpers, you can process all at once. No reason to, though. The advantage of slow food is supposed to be healthy and enjoyable. All parts, not just the eating.
Best wishes!