Look at your needs. If you want to use fitness equipment, choose new ones with good equipment. If you want to keep fit and take a yoga class, choose the course content and time that suits you. There is no best, only what suits you best. The gyms I know in Chaoyang include Hulk, New Power, Yueyimei, max, Horace, Huayun Bath and Qinghe Bay. You can go and have a look and choose one that suits you.