I'm going with the Spartans because of their massive shields, sure its heavy but they trained with it the day could walk on their own two feet.
So carrying the shield is no big deal for the Spartans. The Spartans had so many advantages because of the shield.
They wore no body armor so that it won't constrict their movements and, the shield can act as a leverage-point to do maneuver that others can't without something that heavy.

But something, you guys and gals might or might not have notice, is their cape. It too had multiple purposes. They are most famously seen as a red cape.
They were mostly made of/from wool and/or cotton with or without leather at times.
The Spartans would use their capes to distract their enemies, get the enemies weapons caught in it, and the cape made them feel like Superman....  jk, but the cape were for rank and use for warmth as well.

I would go for the samurai for being prepared and not abusing their bodies. But the Spartans are raised to fight or die.