I like several features of iChat (video chat, integration, stability), but find it lacks the slickness of Adium. Each time I make the jump to Adium, I find myself coming back to iChat for its core functionality.
One free plugin, however, makes the whole experience much more enjoyable. Chax adds a unified contact list (useful if you use multiple accounts, like both AIM and Google Chat), remembers old messages, adds Growl notifications, options for auto-accepting chats, and automatic resizing of the contact list window, among others.
It’s an odd time to be promoting Chax, as it’s not compatible with Snow Leopard, which will be out in 2 days. However, the author’s Twitter feed offers some hope. In response to a question about a beta version for SL, he states: “Not yet. Hang in there for a bit longer.” It will be worth it.