Business class is much more spacious with better food and services, like using the airport lounge before and after travel. Business tickets should be more expensive than economy tickets.
The 2018 Sapporo Snow Festival is held from February 5 to February 12. Air tickets to Sapporo during this period are in high demand and get wild!
If you look for flights on Hong Kong Airlines website for a return ticket to Sapporo, you may better buy the business ticket.
There are only 6 direct flights each day between Hong Kong and Sapporo. Seats are in very high demand during the snow festival. As the time approaches, the ticket price skyrockets. The price for economy ticket shoots through the roof and is higher than the business ticket. If you must travel during the festival seasons, it would be wise flying business!