You have to think about the most common usage pattern-- folks will most likely want to click through a whole bunch of pairings very quickly to register as much

You have to think about the most common usage pattern-- folks will most likely want to click through a whole bunch of pairings very quickly to register as much opinion as possible until they get bored (think about how people use hotornot or kittenwar). You have to make the voting area easy to click (nice and big) and in the same position every time. The photo is the most logical choice. I agree about the explanatory text, but my reflexes are conditioned to stop and read a submit button before I click it, and parsing the text on the buttons (which changes every time with the candidate's name) adds time to the transaction. You could solve this by making the text consistent from page to page, if you're wedded to the buttons.