Remember 3-2-1, 2-2-1 are just guidelines to get you close, and they are based on 225. Definitely don't think you want to go 3-2-1 with baby backs at 250.
Al's method works, especially once you work out what IT at each point give you the ribs you want. And that is a big part of this, do you want competition style ribs with more bite, do you want tender ribs with just a bit of pull, do you want ribs that you can make a mcRib with, or do you want true fall of the bone, can't keep them together to get them off the grill ribs.
It's an over simplification, but in general I look at the 3 stages as:
First stage = Setting the bark, and cooking the meat, The meat is technically done in this stage, but it isn't DONE, unless you want pork bubble gum. If I am happy withe bark at 2 hours I might foil early. If I am not happy with the bark, I might run longer before foil and adjust the other stages.
Second stage = breaking down the fat and fiber and getting them tender, while keeping them moist. This is the easiest stage to adjust what will be the final product. More time and/or more liquid, slides you done the tender scale until you get to "pulled pork that use to be on a stick", but at a lost of bark and bite.
Third stage, firms everything back up and lets you reset the bark or even add to it, but this stage can also overcook, dry out your ribs if overdone. I have done a bit of everything with this stage. Including only doing 15 minutes to just "dry" the surface, and then quick 2 minutes sear on piping hot grill. Sort of "faked" doing a rib that hadn't been foil, it wouldn't fool the experts but would most of the folks in your backyard.
The guys that don't wrap, really have 2 stages. They still got to develop the bark and cook them, and then break them down to be tender, they just do it without the foil, which means they don't need the 3rd step.
You can get good ribs either way, and at the end of the day its all about what you and your family likes.