Power Swap only swaps stat CHANGES, not EVs, IVs and natures. So, Stat changes like the drop from Overheat, Swords Dance, etc. It is the same with Guard Swap. Power Swap is only Attack and Special Attack, while Guard Swap is only the Defense And Special Defense.
Source: Bulbapedia pages on these moves.
Note: I think you are confusing Power Swap with Power Trick. If this is the case, it takes the the raw stats and switches them, so everything that affects the stats except for stat modifiers ( Boosts, Choice Items, etc.) Will be switched. So, This will mean that the EVs aren't switched, but the star value is switched. Hopefully that makes sense. In this case, Shuckle is the obvious winner with 230 base defenses.
Hope this helps!
