AIM for me...i've been using it for a long time, since it first came out, all my friends use AOL and i never did, i'm 18 (turned 18 yesterday!) so i've been in high school and nobody at school has ever had anything other than AOL, except me...so i pretty much had no choice...
when i would ask people what ISP they used they would either say AOL or if their parents set up their internet, they would say netscape (since almost everyone used that browser then...hehe)