Most people have covered it here, but it boils down to your storage needs. Some folks can survive on 16GB. I can because i have a 8X and have no intention of putting much music on my 925 - that's only for photos and videos. For people who want it all, the 920 is best. Now, if you are able to get the Vodaphone 925, then that's an upgrade because all you are giving up is the built in wireless charging (that one has 32GB) for a lighter, sleeker looking model.
I owned a white 920 that I gave to my dad as a gift. I give him that and kept the t-mo 925 because of the fact that the 920 has more stuff out of the box in between the extra storage, and built it wireless charging. He just has to back his pictures up periodically - which he will take a ton because his grandkids (my nieces and nephew) and the neighbor's kids are always around and he is big on picture taking.
Plus in many cases the price difference favors the 920. You may be better off sticking with that.