well I wouldn't say that the MTX3 has a lower CG than the tc3, but it is certainly lower than the mtx2's CG.
FaTaL, it depends on what you prefer.
Despite what others say (deny, admit and grumble about), the NTC3 as it is stock, is much weaker than my MTX2. I won't say more than I feel that the durability has carried over to the MTX3. With 'the fix', or a similar thing to it, durability greatly improves, but I still wouldn't give it high durability ratings. But then again, the mugen's have belts, and if you regularly visit rough parking lots with gravel or small rocks, the belts can get mangled. But the TC3 isn't impervious either, because all cars can get rocks stuck in the clutch bell/ spur gear.
i would be lying if I said no car needed hop-ups, because some feel almost every car needs hopups, while others think in a minimalistic fashion. But, some cars handle differently. The main difference between Mugens and the Associated is in the drive train. The drive train is incredibly free on the tc3, but at my track, I feel that is a huge disadvantage. I drive relatively smoothely, so I drive a lot in between full brake, coasting and full acceleration. However, coasting with a TC3, is still way too fast to enter most turns. You could use drag brakes, but I feel it makes a car feel slightly more inconsistent.
overall, I prefer the Mugen belt cars, but at a different track, the story could probably be different.