I've switched to Discord since learning AIM was due to kick the bucket soon. (RIP!) I was previously using AIM through the chat program Trillian.
So far, I've found I really enjoy Discord; the ability to create servers with separate channels in particular is a really neat feature, and can be used for one-on-one OR a group setting. My biggest complaint is the lack of auto-logging into a text file, though Discord does save your messages and allow you to search (though not by date, as far as I know). The window itself is kind of large and clunky, but that can be fixed with CSS, and new plugins to customize your experience are coming out/being updated regularly. Other than that, I've had a good experience with it so far.
If it's not your style, Pidgin is a good chat client that supports Discord, Google Talk, IRC, Skype, and a bunch of other protocols. (You can find a list
https://developer.pidgin.im/wiki/ThirdPartyPlugins. It's very plain and, in my experience, a little clunky but I believe it's reliable and straightforward.
Hope that helps!