We stayed in the Mercure for 5 nights on our recent Sapporo trip. It is about 20 minutes walk from the JR station, but this can be done completely underground following subways and shopping concorses.
We paid about $US130 per night for our room on average, which was a bargain. Our room was sizeable by Japanese standards and was delightfully fitted out, including the impressive bathroom. The staff were very helpful and friendly and spoke generally excellent English. There was free room internet (both cable and wifi), with each room apparently having it's own dedicated wi-fi.
All in all a great stay, an excellent hotel. There are a wealth of dining options nearby, and I would highly recommend Kuro Shima, which is on B1 of the M-Square building next door. See my seperate review of Kuro Shima for more details.More