MMORPG Keyboard or Mouse?

Recently I have upgraded to a new computer. One of the reasons is to play World of Warcraft. I have a normal keyboard and mouse at the moment and was recently thinking about buying specific ones for playing it. The only problem is I don't know if I should go with a mouse or keyboard since they basically have the same function. I was thinking about buying either the Razer Naga Epic and the Razer BlackWidow Ultimate or the SteelSeries Shift: Cataclysm and the Naga Mamba. Which pair should I get based on your opinion and experience with these Naga/SteelSeries products and their functionality? Please refrain from giving other choices or giving opinions solely on looks.