GWG, Back when I was guiding in Alaska I worked for Brian Okonek of Alaska- Denali Guiding. Brian had a justly deserved reputation as the most experienced and best guide working on Denali. Guiding with Brian was like getting your Phd in Alaskan Mountaineering. On one of the trips I did with Brian we had a client by the name of Colby Coombs. He was a high school senior and, if I recall correctly, had been told by his school that he had a choice between expulsion, and doing independent studies, preferably somewhere very far away from school. Colby chose climbing Denali as his senior project. I really liked Colby. He did a great job on the mountain, went on to guide for NOLS, I think, built a terrific climbing and guiding resume, and later bought Alaska-Denali Guiding when Brian was ready to retire. I believe Colby has changed the name of the guide service to Alaska Mountaineering School, or something like that. Make sure you check them out. Knowing Colby, I'd put my money on his outfit being as good as it gets.
And believe me, there are differences between guide services. I was pretty surprised at some of the shoddy practices I saw on the mountain. Poor, that is dangerous, campsite selection, walking between camps unroped (good way to end up wedged deep in a crevass), weird tie ins, etc. And this stuff was being done by guides working for big name outfits.
-20 degree sleeping bags
A tip on VBLs. I found that if I pulled the thing up over my shoulders it was like a sauna, really muggy and uncomfortable. I found a VBL to be much more comfortable if I just pulled it up to my armpits. I could only stand to use it on the really cold nights, but it makes a big difference when it's colder than minus 15 or 20.
Here I go again. Check out Alaska Mountaineering School's website. Looks like the company philosophy is the same as back when it was Alaska-Denali Guiding. That is, when you climb with them you are taking a course, not just being lead up the mountain. Check out the client's comments, they are pretty informative. Also ask the Climbing Ranger in Talkeetna about the safety record of whatever guide service you go with.