I use Windows Live Messenger its fantastic, widely used and its great.They bring out updates regular to update your software.All my friends use it, its fast easy and free.Ive never had any problems i would recommend it to everyone
I prefer Skype....i'd experienced alot of problems with yahoo messenger..sometimes the voice chat in yahoo gets disabled and i coudnt call someone or receive calls from someone...so i tuned to skype..the voice chat is crystal clear and it has a very good easy to use interactive....