Put the piece of paper away and don't look at it for 24 hours. You may want to take it out again the next day, or you may wake up having made your decision. If you do look at the paper again, look at it from a distance - from across the room. Do any of the blocks stand-out?
If you still can't decide, then bring a trusted friend in on the process. Another person's input can help you see things from a different point-of-view.
Source: Dijksterhuis, A. and Nordgren, L. "A Theory of Unconscious Thought". Perspectives on Psychological Science, June 2006.
