Arstechnica is one of the premiere tech forums that I know of. It has a much more mature feel than the Anandtech forums. I don't know about the other, since I don't pay any attention to that site. Ars is often times mentioned, or quoted by other online sites, especially digg and slashdot, and they occasionally make the national news as well.
It is moderated very closely, flaming simply isn't allowed. The technical discussions fly over my head most of the time, but I still like reading through most of them, especially when they start commenting on microprocessor architecture and future trends. Many of the members are EE's or IT professionals. But there is something for everyone there. Audio, visual, modding, gaming---all of the forums are active.
One of the things that sets it apart is that part of the site is set aside for subscribers. If you just want to shoot the breeze, you have to be a subscriber and post in the Lounge. If you want to debate, there is a forum for that as well.
The Agora has its own set of rules, and is one of the best places for online trading, but you have to read and follow those rules closely. They have three mods who maintain control, but none of the regulars will let you slide either.
It is informative, fun and one of my favorite sites online. I guess that was coming through already.