Reddit gets a lot of stick, but it's a bastion of civility and intelligence compared to the comments on youtube videos or even mainstream newspaper comments. I don't think there is any forum of comparable size that has a higher quality discussion. Reddit's problems are just humans' problems.
Primarily because they way it works, there are lots of high quality comments in smaller subreddits. It would probably be beneficial to filter out some of the default subreddits from the data sets to improve the quality of the data.
