Well, really, /both/ makes sense lore-wise.
This topic feels like it's going to devolve into 'WE'RE THE GOOD GUYS OTHER GUYS SUCK', but, think about where your character would go based on the following:
The leader of the Tushui, those who practice patience, went to the Alliance.
The leader of the Huojin, those who believe the greatest crime is inaction, went to the Horde.
Which belief are they of?
Would they follow their leader, to be of a faction of similar thinking, or go the opposite way of their leader, so that they may spread their ways among a people who might know less of them, and in turn try to learn from those people?
Rather than asking about the Horde and the Alliance, think about your Pandaren as a character. Dante went with the leader of the Huojin because he couldn't bring himself to follow the Tushui. He's not really about balance, or learning other's ways, and he is far from patient, and so the Horde, and the Huojin, fit him well.
What's your character like?