I own a A4Tech Wireless mouse.. A4Tech has the longest battery life.. I Never noticed "lag" to me.. it's the best wireless mouse out there. Uses RF. Not bad. I had it up to 10 feet away.
I was mad at the wires constantly catching my desk.. so i was about to break the dumb dell mouse (did that later).
I Highly recommend A4Tech, They beat every wireless mouse in every test.. And they are very smoooth.. and cheap.. mine was only 20 dollars at a store.