I have used RMI on three different routes up Rainier. They are large, well organized with terrific Guides. There is also some overlap among RMI & IMG. I have not used IMG, but am planning on using them next summer for a Mt. Bona trip. IMG was recommended to me by a well known Guide from RMI. I have also been in Alaska with Alpine Ascents and they are strong as well. My suggestion is to go with the same service on Rainier that offers a Denali schedule you like. It is hard to go wrong with any of these three. All are well organized, well established and responsible, which is not the case for some of the otherwise well know services out there.