One uses an interlocked armor, the other provides protection with a continuous welded sheath. You can get 600V and medium-voltage cable in a wide range of conductor sizes. Flexible metal-clad control cable is also available. The NEC recognizes interlocked armor construction for use in high-rise buildings, places of public assembly and many hazardous locations. An aluminum strip is formed lengthwise along the cable, then the seam is welded.
Corrugations can make the armor more flexible.
In branch and feeder circuits, voltage drops, rather than ampacity, may determine conductor sizing. A simple calculator helps with single-phase estimates. It all starts with Ohm's law. Since a real wire has real resistance, it also has a voltage drop when you pass current through it. In many cases, voltage drop may be a more limiting factor on conductor size than rated ampacity.