I haven't used the x940bt, but I have used several other avic models in the past before getting the SPH-DA100. I really like the appradio2 features with ARLiberator. Google nav with traffic is a great option. Ultimately I like the freedom of using whatever I want to use to display on my system.
For me the only pitfall is that I have an older tv in the back for kids, and the Appradio2 doesn't have outputs to go to the tv like many other pioneer units do.