Speaking for myself, I just do a quick scan of all the other DPS when I play dancer, and I pick the player with the highest item level weapon. If someone has a Pandemonium weapon, or an upgraded tomestone, for example, then it makes me think they're more likely a more skilled player since they're clearing savage. Then beyond that if people are tied, I tend to favor monks since their higher speed means more procs for me, and devilment means more forbidden chakras for them.

But as other stated, I wouldn't take it too seriously in the 24-man. I've seen people leave dance partner on someone who is lying dead on the floor for >50% of the fight. I've seen people dance partner the astro (probably hoping to get more cards?) I've seen people forget to dance partner anyone until the 3rd fight in. A lot of players don't always make the most optimal choices (heck even my own methodology might not be optimal)