In University, about eight years back, the chat programs of choice seemed to be ICQ. The little flower in the bottom of my screen would flash and the speakers would blast out a high-pitched, "Uhoh," every time someone sent me a message.
I eventually moved onto Yahoo messenger, but after a few years, broken by intermittent travel, I gave up on Yahoo. The program seemed to get too complicated, with little applets for hundreds of applications. Games, chats, videos, funny messages, etc, etc. Yahoo messenger seemed to slow my computer down noticibly. It also made the system more unstable, and after a while, the computer started to freeze up.
So I switched to something simpler, a program which seemed to suddenly sprout up and is now a major competitor. Skype offered the basics I needed, and allowed me to make dirt cheap phone calls overseas. I like its simplicity, and since originally downloading Skype, small improvements seem to be made every so often, like smoother call quality, video conferencing and Skype in where I can buy a phone number in any country around the world. I haven't had the program crash on me, and though I've only used the camera twice, it hasn't crashed like Yahoo seems to do.
I also have google talk, because it is an even simpler program than Skype, and because Google tends to do things well. It is conveniently tied into my email account. Problems, I sometimes have delays when calling people. It waits several seconds before connecting, but afterwards the conversations run smoothly.
I prefer to only have the necessities running on my computer. The more programs, the more confusion and possible conflicts. Keep the basics running, and the rest will be easy.