If you are looking for the best of the best, and don’t mind paying for it, Sushizen (すし善) is one of the top, high class sushi restaurants in Hokkaido. Depending on the type of sake you are drinking, an evening here will set you back around 30000 yen, but the experience can definitely be worth it. The attention to detail, the interior (especially the Maruyama location) and the service are top notch. Even the green tea, the fresh wasabi and the miso soup taste much better than your average sushi restaurant. If 30000 yen is out of your range, going for lunch and asking the sushi chef to serve you for under 10000 yen should not be a problem. If you would like to entertain guests for business, then this might be the place to go.
Maruyama location: Nishi 27, Kita 1, Chūō-ku (open Google map)