I love Adium, but I don't think anyone would argue the point that it does not support all features of the current release levels of the clients it emulates -- AV is the most notable exception, but in the case of MSN, there are some other things as well.
Outside of iChat and AIM, and I guess, Skype, there are really not a lot of options for AV chat on MacOS. aMSN appears to be bridging that gap, and I believe GAIM will as well, eventually opening the door for Adium to provide this, but today, that is not the case.
Nonetheless, for text IM, I absolutely adore Adium, and would not leave it for any chat software, with the possible exception of Trillian.