Neither. I suggest a corded mouse. 1) Cordless mice typically have a delayed response. 2) Cordless mice become unresponsive if they move out of the range of the receiver. 3) Cordless mice are heavier, as they carry the added weight of batteries. These three things will only hurt your FPS gaming. 4) IMHO, cordless mice are a waste of batteries (and money since batteries aren't cheap--and neither are the cordless mice themselves). This, of course, isn't great for the environment, and the money you spend on batteries equals less to spend on FPS games.

I would suggest the
Microsoft IntelliMouse Optical (which I use), or the
Microsoft IntelliMouse Explorer. Both have 5 customizable buttons (can be mapped to almost any keyboard key, meaning you can actually use all 5 mouse buttons in most games) and scrolling wheel (which doubles as the 3rd button). Both are optical, meaning consistant movement without need for cleaning. And both (check back of box to be sure it's the latest version) have 6,000 image per second scan, meaning moving the mouse too fast will
much less likely result in the problem associated with slower optical mice (most only scan at 1500-2000 images per second).
Don't be fooled into thinking that heavier mice are "better built" or "more solid" than lighter mice. Optical technology doesn't make the mouse's required components heavy at all. A heavy optical mouse is likely so
only because the manufacturer adds heavy metal weights. I think lighter is better, especially in FPS gaming.
If you'd like to go with the Logitech brand (I much prefer Logitech's joysticks over Microsoft's, so don't think I'm an M$-only product fan) I'd suggest the
MouseMan Dual Optical. I'm skeptical of the "Twice as fast, twice as accurate" claim, when it comes to the fast part. Each sensor can only compare its current image with its (and not its counterparts) previous image. I could see the dual optical sensors being more
accurate however, but only on some surfaces which may return slightly changing images to the sensors, like maybe on carpet.
Keep in mind that the Intellimouse Explorer and the Mouseman Dual Optical are right-hand only mice. Whichever of the three feels most comfortable in your hand is probably the best choice.