Which one is the best/biggest one?

The 5th one - Badaling Ski Resort, covers an area of 3000,000 square meters, maybe the biggest. With complete facilities, you may experience the foreign custom here. I do not think this ski resort offer shuttle bus services or pre-booking cheaper price, but the direct bus No.919 is available between urban area and the resort. And the resort often offer the preferential price, you may check with them for details.