Well both of their people absorb solar radiation. However, Starfire can take Solar radiation from others which caused her to weaken a few kpytonians. She also has fighting combat skills. However, there is also the issue of speed. Not sure how fast she can go. She also has her starblots. She is durability and a healing factor


Superman gets stronger and stronger from the sun. Can move the earth and turn back time. Can run faster than a speeding bullet. Has a healing factor/


I mean really the only thing I somewhat think what gives Starfire a upper hand is the fact she can still his Solar radiation.