I check all the bitcoin forums twice a day. Have to stay current and get inspiration for new blog articles. Also reddit. I have noticed two trends over the past few weeks. Bitcointalk is losing popularity. Forum.bitcoin.com is holding steady. On reddit /r/btc is now the most relevant subreddit for bitcoin discussion once you separate the wheat from the chaff.
The most intriguing change I have seen is the trend towards using Slack. Bitcoin Classic has come from nowhere to prominence in a few weeks just using Slack. Yes they have a subreddit and subforum at bitco.in but all the action is at Slack, not a forum or irc.
Even miners are starting to contribute to Bitcoin Classic on Slack. If Classic is successful in replacing Core it will be the first time I know of that a project was popularized and became number 1 using Slack. Slack is also easy to use on a phone. While you can use it on your laptop I usually just access on my Nexus. It is not a memory hog so I leave it running all the time to avoid the hassle of logging in/out.