Third floor. All right. The third floor of Ningbo Olympic Sports Center is better than the second floor for the following reasons:

1. There are gymnasiums, badminton courts, basketball courts and tennis courts on the 3rd floor of Ningbo Olympic Sports Center, which can meet the fitness needs of different groups of people.

2. The 2nd floor of Ningbo Olympic Sports Center is mainly a commercial area, and there is no sports ground.

3. To sum up, the 3rd floor of Ningbo Olympic Sports Center is good.