I prefer wired. My Razer Lachesis has served me very well throughout my gaming forays. I love it so much. It was giving me issues a few months ago but now it's working rock steady.
Wireless as long as it is Gamer Certified. If it's just some off the wall common use wireless mouse you find at walmart, no. If it's a gaming mouse it's made for a gamer, data transfer speeds, battery life, and performance in mind. Average wireless mice have a much slower data speed.
Wired Mionix NAOS 8200 Built so much better than any Razer mouse I've ever owned and cost just as much as a Naga. Although, gotta hand it to Razer for making a mouse like the Naga, cause I can't play any MMORPG without it.