I think they're mostly consistent within each series. The Anniversary line is a different, bizarre thing because most of the first wave was just a bunch of lazy re-releases of Halo 3 toys.I just want a Collection of the series iconic characters at the same scale, mcfarlane increased the scale with the reach figures with the reason "it allows for us to add more detail to the characters" that is fantastic and it actually came true, reach scale stuff is pretty decent, but along side this they ship a seperate line of figures under the "Anniversary" title that are much smaller than the reach scale except a spartan model which is the same size as the reach Spartan III's.
The mcfarlane scale is all over, it changes per figure not just per wave. While NECA dont make true action figures in the sense of how many articulation points what they do make is decent quality models and everything from the AVP/GoW/Bulletstorm/Duke Nukem lines are good quality.
I dont see why mcfarlane needed to change the scale Again for Halo 4 when the reach scale was fine. All they needed to do was keep that and release the ODST and Human characters in that scale.
I'd like to see some more comparisons of the H4LO figures, as well as comparisons of their in-game sizes. I'm not even sure if it's an issue of actual "scale" as it is blindly making human/alien figures the same size as their Reach counterparts.
The two lines' Spartans' proportions are mostly identical, seemingly ignoring their Mark number.
Pics from halofigures: