Long gone are the days when IRC was popular.
Nowadays, the servers that where highly populated are just empty.
Here is a top with the most populated irc servers, today. (stats where taken at peek hours)
1. Freenode: 1700 users (most populated channel). There are mostly programmers’ channels on this irc server.
3. Rizon: pretty populated. The biggest channel has 1800+ user. Channel #news. There are many 100+ users channels.
4. DALnet: a bit more populated than Undernet. There are a few channels with 100+ users.
6. DALnet: a bit more populated than Undernet. There are a few channels with 100+ users.
7. EFnet: around 10 channels with 100 – 500 users. Mostly gaming.
8. Undernet: a few channels with 100+ users. Highly populated, around 2000-2001.
9. GameSurge: just three channels with 100+ users. Gaming server.
10. IRCnet: three channels with 100+ users. Two with 300+. General talking. I think that this is the official irc server.
I’ve tried other irc servers besides the one from the above list and they seem pretty empty. They don’t even have 100 users on any channel.
You can hunt populated channels by going to “Tools” > channel list > get list (when being connected to a server).
If you want to stay on irc and chat, either go to freenode or quakenet, these are the best choice.