tieba.baidu.com

quora.com (a quasi forum because it uses the Q&A form) or reddit.com

Tieba is definitely most popular comprehensive forum but there are also forums focus on one topic where discussions are more serious and deep. Mine favourite is zhihu.com though it's already in decline. It uses Q&A form, more serious than reddit but more jokes or junk information than Quora.Much college students users and topics on natural science or IT is heated. Douban groups is also great but ..It had declined for years. 天涯 www.tianya.cn(gossips,conspiracy theory,supernatural stories, even history or military once) It had declined for several years. 虎扑http://bbs.hupu.com/(sports)