I have the 3.0 that I ordered with my computer. It works really well and I like it. I tried one of the 4.0 ones at best buy, and I didn't really care for it too much. That new side to side scroll wheel puts too much space between your fingers and it's almost like you have to stretch them apart to fit the contour of the mouse. It's rather uncomfortable actually. On the other hand, the only drawback I find with the 3.0 is that it just feels cheap. I don't know how to explain it really, it just feels like it was made with the intentions of best appearance and not quality. Anyone who's got one probably knows what I mean. I prefer logitech mice over any other brand. I have an MX500 that I use with my desktop, and I feel that it works better and is more comfortable than any of the microsoft or other brand mice.