Per a 2020 study by Daniel Potter, PhD and Daniel Baker, PhD - both Professors of Entomology, monarchs preferred laying eggs on milkweed that was planted at the perimeter of the garden (the first option in the photo), and had a harder time finding milkweed that is mixed in a more "feral" type planting.  Other preferences they noted:

• Monarchs are visual creatures and identify their host plant (milkweed) by the shape of the leaves and the plant itself. It helps to set the milkweed off by mulching around the individual plants.

• Taller species like showy (speciosa) and swamp (incarnata) were frequented up to four times more often than the shorter species like butterflyweed (tuberosa) or antelope horn (asperula).

• The gardens with unimpeded north/south access had more visitors than those without.

• "Nativars" are a cultivar of a native species, and did equally as well with attracting monarchs, and with no downside per this study. Some examples are shown in the photo to the left.