I recently had a decision to make on what insulation to use on a basement area which I was finishing out with 2x4 walls. After calling a couple of other contractors (electrical, plumbing) I knew and trusted to get their recommendations for an insulation contractor (I asked them who they would use if they were building), I narrowed it down to two. One really didn't want to do this size job unless they were also going to do the rest of the work (rough in, sheet rock, etc.), so it was an easy decision to use the other gentleman, who was very good to work with.
Here is what I learned from the process. The insulation contractor I used explained that R values alone could be misleading. His example was this in the form of a question-what is the R value of an ice cube? I replied zero, and he then asked me how it is that an igloo can keep you warm? His point was that air infiltration was also critical, and that a lower R value with a good air infiltration barrier will stay warmer than a higher R value with less of an air infiltration barrier.
Given this, it made it pretty easy to choose a skim coat of close cell insulation even thought it was more expensive than open cell, and then fill the wall cavity with blown in out to the studs. The total surface area was about 1200 square feet, and I'm estimating that they did at least 1 1/2"s of foam. By far this is the most comfortable room in our home.
I looked at the cost ($1900) as an investment, and I only wish my entire house was built this way. If I every build anything in the future, this is the only way I would do it, unless something better comes along.
GGB