>>350622241
>mesh toggle
More meshes means more cost to performance. While the mesh is off there is no cost to performance at all because it's not being rendered.
If you're going to keep it off most of the time, this method is best. If you're toggling entire outfits so each outfit is base body + outfit for a total of two meshes active at once at most, it's definitely not bad either.
>shapekey
The entire mesh is still being rendered even though it's behind another part of the mesh. Same poly count but less meshes is more performant but because you are still rendering it with it "hidden" it's less performant than the above method while hidden and more performant while it's active.
>move UV to a transparent part of the mesh
Transparency is more expensive than opaque rendering and the mesh is still there and being rendered even though it's see-through. This is less performant than shapekey method but does mean you don't need to touch blender to get it to work so japs like it. Making shapekeys isn't hard so please don't use this method it's fucking retarded.
>materials change to transparent
Same as above: mesh is still being rendered and transparent so it's expensive but this time it's another material instead of a section of one so it's another draw call.

All in all I'd suggest small pieces that are often going to be on should be toggled through shapekeys but large pieces by mesh toggle.