The microporous layer is the superior coating used for inkjet photo papers. The coating has micro pores or nano pores which are silica or alumina based.
What is important to note is that this coating, due to its pores, can accommodate all type of inks; dye and pigment and can cope very well with the particles in the pigment inks which sits well in or on the pores of the microporous coating.
RC paper is normally instant dry and water resistant. The microporous coating will provide a better colour definition with a deeper, more solid black than the cast coated paper.
Quality of course, varies between different manufacturers and some will provide better quality imaging than the others