I don't even remember which hotels UA has put me up at NRT, but they've all seemed OK (fine, not spectacular). With their own airport bus services. If UA hasn't already given you your vouchers, and they don't have them for you as you step off the plane, plan to go to the RCC--they'll be there (in my experience--in this case you want to follow the signs for transfers rather than arrivals). For your next day's flight to SIN, you can also use the ANA lounge (down the hall from the RCC).