There’s no perfect approach. Visibility and quality are both important. If public voting is the method of choosing a winner, then visibility is all the more important, although it still needs to be a good meme. If “quality of the meme” is the most important factor, then the winners ought to be decided by someone or a few people (like a panel) judging them based on specific criteria, such as how this one requires the meme to include the Bitcoin Rocks sign. Similar to the Olympics. As for me, I try to equally repost my own entry and the main contest thread throughout the duration of these contests.