XR-E lights are talked about have great throw especially the R2.
XP-G has great flood and the most lumen per Watt.
The thing is the XP-E sits right in the middle for me has good throw and flood, and does not have the ugly cree rings. Also the transition between the hotspot and the flood is smooth. The XR-E light tend to have a tight hotspot adn little flood, while the XP_G have nearly all flood and barley no hotspot, also some have a dark spot in the middle. Some XP_G and XR-E tend to have Green or Blue tints.
As long as the reflector is correct, xp-g's look the same as xp-e except the hotspot is larger (but not brighter), and the spill is somewhat brighter. If you use focused smooth reflectors, it's pretty obvious from the characterstic well-defined circle in the middle.
Generally a lower vf is a good thing, but in the case of xp-e, it means that a direct-ish drive will tend to overpower the led compare to the higher vf of xr-e's or higher capacity of xp-g's. This happens when you use 14500's in an aa light.
So an xp-e is better for AA only lights, and xr-e may be better for 14500's.