I probably prefer the UFO:AI system. Because the TUs to fire, move etc stay constant, and the actors TUs rise, they can do a little more per turn, over time, which seems entirely in line with real word experience.
One of the main advantages of elite soldiers is that their training allows them to execute missions quickly and efficiently, with a minimum of personnel. It's not necessarily that they do much differently to a regular soldier, but that they are capable of doing it faster, always being ready before the other guy.
So, as PHALANX troopers get used to fighting the aliens, and given the UFO spawn rates, that they see more action in a month than some SF troopers do in five years, the ones who survive would be getting very good.