The Revoltechs have a 3D torso joint, which I think is pretty critical to dynamic looking poses. I agree that the hip joints are lacking, but in terms of good looking poses that doesn't seem to have as much of an effect as the lack of torso joints on GNUs. The pivot point on the thighs help immensely as well--you can't really do the Revvy YF-19's flying kick pose on a GNU YF-19 because of it. Kaiyodo seem to have a lot of experience at strategically placing joints for the most dynamic poses and working around limitations.
In all other counts though, the two lines appear equal in articulation (okay, minus the GNU YF-19's crap knee bend). GNUs have ball joints where they count, such as at the shoulders, hips, and ankles, and all Revoltech joints are--functionally--ball joints as well. Big plus for the GNUs is that, having actual ball joints, they're much easier to pose and have a finer range of motion. Revoltechs are more difficult to pose (as evidenced by the YF-21s in this thread that look like they've had their limbs broken and/or half pulled apart) but they hold better plus the whole modularity thing.
That said, the way the GNU YF-21 looks at 3/4th profile is atrocious, I can't believe they screwed it up that badly even though the lineart shows it at that angle. And someone must've been drunk when they came up with the placement of the YF-19's leg skeleton in relation to the armor, if they'd moved it up a centimeter it would look practically the same and have almost twice the range. The Revoltechs don't really have glaring/obvious/stupid errors, but their sculpts are definitely funkier than the lineart and of course the intrinsic disadvantages of PVC (ABS? POM internal skeleton? Why THANK YOU YAMATO). You can really tell that Kaiyodo's guy's actually a designer though, and recognized and captured the spirit (if not the exact proportions) of the lineart, while whoever did the GNUs sort of mechanically tried to copy the lineart exactly.