Hawley-Dolan and Winner asked 32 art students and 40 psychology students to compare pairs of paintings. One piece of each pair was the work of a recognised artist, such as Kline, Rothko, Cy Twombly, Gillian Ayre, and more. The other came from the oeuvre of lesser-known painters, including preschool children, elephants, chimps, gorillas and monkeys. The paintings were matched according to colour, line quality, brushstroke and medium; the students had to say which they preferred and which was better.
The short answer is that the student preferred the professional art. Full story at the link above.