(well clients I’m showing down can be installed also in Windows or sth else not just for Linux.. )
3 Best Messaging Clients :
1.Emesene: is an open source instant messaging client designed for use with Microsoft .NET Messenger service.It is a clone for Windows Live Messenger designed to work with Ubuntu Linux operating system. Its goal is to replicate the functions of the official Windows Live client in a simpler, cleaner and easier to use interface.
2. Empathy: is a messaging program which supports text, voice, and video chat and file transfers over many different protocols. You can tell it about your accounts on all those services and do all your chatting within one application. Empathy is a multi-protocol instant messaging client for Ubuntu Linux with support for Google Talk (Jabber/XMPP), MSN, IRC, Salut, AIM, Facebook, Yahoo!, Gadu Gadu, Groupwise, ICQ and QQ , so somehow its [All in One] (Supported protocols depend on installed Telepathy Connection Manager components.) Supports all protocols supported by Pidgin.
3. 
Pidgin: Most of the people have used this client on Windows as well. It is the default instant messaging client that comes preinstalled with Ubuntu right now with support for over 17 different protocol services like Msn, Yahoo, Jabber, Google Talk and much more.
You can also install them by entering commands :
# sudo apt-get install emesene
# sudo apt-get install empathy
But Empathy usualy is inside Linux Dsitributions
and :
#sudo apt-get install pidgin
Or install all at a time :
#sudo apt-get install emesene empathy pidgin
Altin Ukshini 