the 85mm f3.5 is a dx lens, it has macro focusing so you will be able to get to within inches of your subject for a lifesize (1;1) image.
the 85mm f1.8 is a fx lens. you will not be able to get in as close as the former lens. it has a much larger aperture letting in more light when wide open.
either should be good and sharp. the dx being designed for macro and the fx more for portrait work.