I used American Alpine Institute. Frankly, I don't use anything else these days. They were absolutely first class. I made some great friends (both guides and clients) on that trip that I still climb with 6 years later. I found them to be humble, patient, like able, and extremely qualified, both as climbers and leaders. I think the owner, Dunham does a great job with that outfit and his Denali trips are certainly a highlight...
And just remember, on Denali, they don't carry your shit. They cook the meals, but you do the dishes. They make decisions on the weather, as they should --- especially if you're not from Alaska. But other than that, you'll be climbing the mountain as if you would normally. I enjoyed my rope mates and thought the guides were great too. I still look back on that trip with extreme fondness and would do it again someday for sure... Although the Rib looks too good to pass up... .
Sorry if it sounds like an advertisement, but they have been very good to me over the years. Can't say enough...