I wrote a PHP script that runs 24/7 and shows me leaderboards for all coins traded on Poloniex, by various time periods (not just day, like you see on poloniex.com).  This is what I see a few minutes ago, top coin for each time period:

2 hour change: EMC2
4 hour change: EMC2
6 hour change: EMC2
12 hour change: EMC2
day change: EMC2
2 day change: EMC2
4 day change: EMC2
week change: EMC2
2 week change: EMC2
month change: EMC2
2 month change: EMC2
3 month change: EMC2
6 month change: EMC2
year change: EMC2

:-)