.......i think it goes through coinbase and gemini and shape shift. Poloniex does have the biggest selection but there are only a few major players that people are seriously purchasing and you can find most on other exchanges.
However maybe there is a correlation between Ether, Ripple and Poloniex because its not on shapeshift or coinbase and there arent any trust worthy ripple wallets
Ethereum deposits/withdrawals are disabled on Poloniex and other exchanges, because of network problems. This caused low trading volume. I write about that https://steemit.com/crypto/@joewing/eth-network-instability-caused-by-ico-and-its-direct-effect-on-price-20
thanks for the info joewing