GPS for me.

After a trip with a friend that has an 8320, I found the wifi and UMA had too many variables to make it a standard reliable service. He had to find an open wifi network that was non-pay, and then only when cell signal warranted it (too low), even then he had some issues with the network/router/gateway config.

On the flip side, I have had zero issue with my 8310 GPS. I refresh when I get in the car, after being indoors, then off I go. Its very simple. And I agree with the posts above, I have no need to add another piece of hardware, thats why I went to an 83XX to begin with. Fewer extras to carry with me.