[Raine24]

Right there on the "No IMO necessary" wagon. The Mark III is the last armor (except maybe VII) to be designed with any kind of consideration for how it'd function as an in-universe object and physical suit. It's got a verisimilitude almost everything that came after lacked, and the people involved in its creation had background in practical effects. It's still the most aesthetically pleasing and, frankly, believable of the armors.