I think I see more compliants with the frame finish on the 642 vs the 442 and it's relatively easier to touch up the black.

However, the steel parts(barrel, cylinder and crane assembly) on the 642 are stainless steel, whereas the 442 are blued carbon steel.

I prefer the 642 for to its rust resistance since I'm more concerned with rust and corrosion of these parts compared to finish wear on the aluminum allow frame.