Those two models represent wildly divergent approaches. The Neuphonix model looks like it follows more of a traditional Toole/Olive/Harman approach, like most domestic speakers, while the Megaphonix appears to be more of a high output, controlled directivity typically used in cinemas or larger venues. Which is right for you all depends on your room, your goals, and determining which is the better tool for the task at hand.
Your questions are pretty broad and concern the range of trade-offs and compromises inherent to speaker design. One of the biggest balancing acts concerns sensitivity, extension, and cabinet size, where achieving two of those criteria comes at the expense of the third. This is referred to as Hoffman's Iron Law. Sensitivity bears directly on the dynamic range goals you're trying to hit. Overall bandwidth, linearity both on and off axis, directivity matching, the overall power response, and more, all factor into design choices, such as driver complement, loading alignment for the enclosures, crossover points between drivers...it's complex, and you would probably need to read Vance Dickeson's book on speaker design for a comprehensive answer to your questions.
Using your two linked examples makes for interesting comparative case studies, particularly given their disparate design choices. You can see some of those design choices in action. Compare the speaker's sensitivities (Megaphonix is far more sensitive), extension (Neuphonix digs a little deeper). Compare the overall bandwith (Neuphonix far more extended in the highs).
Without a full suite of measurements, what follows is just conjecture, but the Neuphonix likely exhibits broad dispersion, while the Megaphonix is more narrow. I suspect the Neuphonix had linearity as a high priority, while the more high output oriented Megaphonix might be a bit less linear. The Neuphonix demands a more burly amp than the super sensitive Megaphonix.
Which is better? Don't know. But they are different tools suited for different implementations. Which is better *for you* depends on your room and what you're trying to accomplish.
