question about retopology

Hi. In short, both are bad with MD's quads being worse. If you want good uvs and good topology, try MD's new retopology tool

MD's quads do not follow the shape of the mesh, which is very bad. You can end up with a 50k tris mesh that still looks like crumpled paper because of this.
Zremesher is not made for retopologizing meshes for gaming, it is meant specifically for retopolizing manifold (no holes) objects sculpted in zbrush. Those objects do not need to morph, move or have polycount limits.
So if you will ask zremesher to give you a low poly version of MD's garment, it will not give denser topology to the breast area that needs to expand or the collar that needs to be smooth. The back area, which is flat, does not morph or bend, will be denser than needed. It will not put an edge loops exactly where elbows, armpits or knees are so that the mesh bends nicely there. Zremesher offers tools for defining density or edge flow but they are pretty useless, the result never looks good.
All of it may not sound like a big deal until you end up with a mesh that is much denser everywhere because it was not dense enough where you needed it to be.

Anyway, if you are making simple items, you can get acceptable results. If you want to preserve the uvs, divide the mesh into polygroups first, tell zremesher to preserve them, then transfer the uvs in blender from the original, the same way you do it with uv_1