Primarily GChat for regular text-based chatting, since I'm going to read my e-mail anyway and a lot of friends also use it. AIM Lite comes in second, but lower than it used to since fewer and fewer people sign on to AIM these days. I use Skype for video calls and audio calls but am not logged on to it all that often. Often it's a case of I'm already talking to someone on GChat and we decide to Skype, or I'm talking on the phone and we decide to Skype since it's cheaper. I also use GChat occasionally to make phone calls since it's free to call to regular phones in the U.S. and Canada from anywhere in the universe.