libgen.io has some advantages. In my opinion the best advantage is that the search results also list the format of book results. It is easier to find a particular format, like epub. You can find out the format on libgen.pw, but it takes an extra step, involving going back and forth between the search results page, and individual book description pages.

That said, as of this moment, libgen.pw is up, even if libgen.io isn't.