I prefer MSN, but most of my (local) friends use Yahoo.
So I use Yahoo for chatting to friends and MSN for chatting to my cousins or people I haven't met before.
Although I get more use out of Yahoo my favourite would have to be MSN.
I have always used MSN Messenger, and I still do a lot. It does happen that I use Google Talk when I check my Google Mail if my friend happens to be online, but otherwise I don't actually have Google Talk installed. It's good, but not much point to installing it when only one person I know uses it.
Ah, and I use the 7.5 version of MSN Messenger. The new "Live" version is quite buggy, kept crashing on me, and likewise with other people.
I definitely use MSN or Windows Live Messenger as they call it now, it's by far my favourite. I used to use AIM and Yahoo, but they both slowed down my computer so I said 'nevermind' to those and I have stuck with MSN since then.
I have Windows Live Messenger (With MSN Plus!), Trillian, and Google Talk. I use Trillian to talk to people I know who use AIM and I log onto extra MSN accounts with it too. I log onto Windows Live with my main MSN account to use all the features. I have Google talk, I don't know that much people who use it though. I like it mostly because it tells you if you have new mail (even though there is something for that already). I talk to people who have yahoo on either MSN or Trillian (with my YIM account).
I only use windows live messenger because most of my friend have it.
Technology is a process the vessel uses to perfect itself.
Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality.