I prefer the forums. While chat has the advantage of posts happening in real time, you can get answers to your questions faster and you can get to know some people better, you can write longer posts in the forums and take your time to analyze things, and you can also edit your posts later. The conversation can also keep on going in the forums. For example, if you want to create some discussion about something, you can make a thread about it in the forums, and it may go on for months without dying, but that same conversation most likely dies very quickly in the chat (most likely in less than an hour), whenever the conversation changes to another topic.

EDIT:
Quote Originally Posted by www.dictionary.com
fo·rum Audio pronunciation of "forums" ( P ) Pronunciation Key (fôrm, fr-)
n. pl. fo·rums, also fo·ra (fôr, fr)

1.
1. The public square or marketplace of an ancient Roman city that was the assembly place for judicial activity and public business.
2. A public meeting place for open discussion.
3. A medium of open discussion or voicing of ideas, such as a newspaper or a radio or television program.
2. A public meeting or presentation involving a discussion usually among experts and often including audience participation.
3. A court of law; a tribunal.
I'd say both forums and fora are valid.