I have both (Microsoft corded optical + Logitech cordless optical). The MS is very nicely designed and fits hand great, as well as having 5 buttons (versus 4 on LG). However I can't overestimate how good it feels not to be restrained by the cord (snagging, catching, etc..,). The only thing to beware of is that if you are installing new OS and drivers the optical cordless can be a pain in the ass especially if plugged in USB port.
Final vote - Logitech Cordless
BTW, My MS Intellimouse Optical did break but it was 100% my fault. I was moving furniture and the cord got snagged and it was crushed by my desk as I moved it (damn cords!). Otherwise it seemed very durable.
