Fire
"HERMIONE!" Harry yelled. The smoke from fiendfyre obscured his vision and he couldn't make out her figure any more. His heart beat faster and faster- had she been consumed by the crackling flames? Every moment he wasted was another second for the fire to advance, and he clutched the broomstick tight.
"HARRY!" There! Her voice, muffled by the smog. He shielded his face from the heat and dove off his ledge, flattening against the stick of the nimbus.
"POTTER!" And there was Malfoy, in the opposite direction.
So of course, he chose Hermione. And she was there to comfort him in the night when he woke up screaming.