I actually really like the design of the MGS4 costume. I like it more than the regular chassi from mission 0 as I don't like the human looking jaw / hands. The only thing I don't like about it is the no claws on the feet, it looks so much more badass than regular cyborg feet.
Other than that or on par with that is the Desperado one. Especially paired with the HF Muramasa, it looks extremely nice.
Oh great Kirby, destroyer of worlds, we are not worthy.