The other two work off the energy of the user's body. This mod lets you wear Halo armor in Fallout 4 The irradiated Commonwealth of Fallout 4 is an often hostile environment, and not just thanks to the ghouls, deathclaws, and super mutants who call.
It can also power itself for over 200 years before it needs a recharge, but it does need to refuel. It protects you from the biggest hazard around (radiation) and it can take a 120mm tank round to the chest and the user will simply stand back up. Anyone with a little bit of training can use it. The power armor from fallout is weaker than either of those, but it's still damned impressive in it's own universe. It's got the armor that's even better than T-51b, and a built-in AI-based super computer that helps you out with stuff, though Cortana isn't as impressive as the Nanosuit AI. Mjolnir armor is amazing but it also requires the user to be a genetically and surgically enhanced super soldier of the highest order. It gives you armor that's nowhere near as good as T-51b, but it's also got strength, speed, cloaking, and a built-in AI-based supercomputer that can help you with whatever you need up to and including genetically engineering and manufacturing a cure to an alien virus.
The nanosuit is the best because anyone can put it on and use it.