What type of chat service is your most favorite and often use online? I've been sticking to Yahoo messenger most of the time because all of my contacts are stored there.
I chose Yahoo Messenger, because the service that I always use wasn't on the list. I use Meebo, because it enables me to be logged into both my personal account, and my networking account.
I do not use any of the above, I run Trillian since I need more than one user connected to X IM client at any given time. Of those able to use I think I use MSN and AIM the most though, not so much the ICQ now (a decade later).
I wish Trillian was included on the above choices. I didn't think of listing a messenger service that runs multiple chat messengers at a time. I have used it before but I still prefer Yahoo.
As a stand alone messenger service, I use AIM the most because I have a lot of people on my buddylist that also use it. I am another Trillian fan because I have contacts on Yahoo and MSN that I want to be able to access and it's easier to have Trillian than to have each messenger installed and on at the same time.
I will choose MSN/Windows Live Messenger as I think it is easier to use and I have all my contacts saved in it. I think it is basically the habit as the people who have used Yahoo messenger use only Yahoo messenger as they find it easy to use and as I have used MSN/Windows Live Messenger from a long time I will prefer the same.
I will definitely vote AOL as I think this is the best one and I am using the same from a very long time. I have all the features that I need and I am quite happy about it.