I think that they have an almost identical feature set.
I really enjoy the navigation style a lot. I absolutely love the search capabilities, where I type in...say best buy...and then it gives me a list of all of them in the surrounding area. Google maps does this with the "push pin" style, I happen to like the list better on the phone. I then LOVE how it gives you the smart options after you select the search result - directions to/from, call, see on map, etc. Again, all of this is available in google, however I find their interface much more clunky.

Also, I really like their directions model, how you can switch between map/list. I don't see that as an option on google's.

My biggest beef with WLS is the startup time...but it's short enough that it doesn't stop me from using it. I don't use it for navigation, I've got tomtom for that (which I almost never use anymore after WLS).