A monohybrid cross involving a homozygous dominant parent (e.g., RR) and a homozygous recessive parent (e.g., rr) would best illustrate Mendel's Law of Segregation. The F1 generation resulting from this cross would be heterozygous (Rr), and when self-fertilized, the F2 generation would exhibit a 3:1 phenotypic ratio, demonstrating the segregation of alleles.