Rather than posting this in a poll form, I'm just going to leave this open for discussion: What IM client(s) do you use (and why)?
Despite all the other "techie" software I use (Opera, foobar2000, etc.), I still stick with the official AIM client (whatever the absolute latest release (beta if available) is) (currently 5.9.3702). I'm a sucker for the latest and greatest functionality (an upgrade junkie?). I don't care for the "IM Expressions," (meh for frilly stuff), but it doesn't really get in my way, either. While some complain about the ads, the fact that they're taking up about 80 of my 1200 pixels of screen height doesn't bother me enough to switch to something else. Furthermore, I've yet to see another AIM replacement that
actually supports direct IM or file transfers as well as AIM does. Lastly, AIM's support for SSL certificates (.p12) is quite fantastic for me, ever since I've gotten paranoid about various semi-public networks potentially listening to me.
I've also recently started using
Nalsoft AIM Log Manager which is a non-invasive 3rd party add-on to AIM that does what it claims to do (logs conversations). Logging was really the only feature that I discredited AIM for not including, but this was able to remedy that complaint without sacrificing the features of the official AIM client onto which I've been so dearly holding.
I use the AIM protocol (rather than ICQ, MSN, Yahoo, etc.) mainly because it's what everyone I know has (which is kind of a circular argument). I live in Minneapolis, MN, USA, and virtually everyone around here seems to favor AIM. I've observed a lot of people from Wisconsin using MSN, but I don't claim my sample is representative or unbiased in anyway (just a casual observation). I used to hang on to ICQ, too (well, maybe around '97-'00), but pretty much everyone I knew on ICQ had AIM as well (and more people had AIM), so it lost the battle.
I tried Trillian for a few weeks (admittedly this was probably ~2.5-3 years ago), and wasn't tremendously pleased with its offerings. I didn't like the appearance (I'm very minimalistic, classic style), it didn't have good feature compatibility with the official clients, it lacked some features, and then it had other features I didn't want at all... I understand that quite a bit has changed in that time, and I should probably give it another try (maybe in a VM), but for the time being, official AIM it is...