We're using the com.google.gwt.geolocation.client.Geolocation class in our demos.
From the PhoneGap documentation, it appears that it doesn't matter which GWT wrappers you choose, because they actually wrap the same (W3C standard) API:
This API is based on the W3C Geolocation API Specification. Some devices (Android, BlackBerry, Bada, Windows Phone 7, webOS and Tizen, to be specific) already provide an implementation of this spec. For those devices, the built-in support is used instead of replacing it with Cordova's implementation. For devices that don't have geolocation support, the Cordova implementation adheres to the W3C specification.
Whichever way you go, see the PhoneGap docs for some hints about Android (your app needs to request permissions in order to get full GPS location accuracy).
Hope that helps!