There are a few websites that publish measured lens data like dxomark.com or photozone.
Other sites list personal experiences and/or opinions.
If you plan to buy a macro lens, make sure that it has the ability to reproduce the scale you need, e.g. 1:1. Many “Macro” lenses only go to 1:2 which means that you’ll also need an extension ring. Longer focal lengths give you more space to work and require more distance for the reproduction of the glass plates. This means that, depending on what kind of setup you use, you might prefer longer or shorter lenses. Lenses can also have a different focal length at short distances. Check out the specified min. focusing distance.
My personal advice is to get a lens with a tripod collar, specially if the lens is heavy. This can be an extra cash-out.