I have stayed at the Sheraton twice - very nice (good restaurant) and there is an elevated walkway from the terminal directly to the front door of the hotel, so you need not go outdoors.
At MUC, I have stayed twice at the Kempinski MUC, which is adjacent to both T1 and T2 (no need for a shuttle):
http://www.kempinski-airport.de/en/hotel/index.htm
Very nice modern decor, comfortable rooms, nice bathrooms

Not inexpensive, but worth it IMHO (especially if you can snag one of their frequent specials / promotions).