No where that I am aware of has lower fees that Poloniex, but I stopped using it some time ago as fees were not enough to justify some of their other flaws. That was before Goldman Sachs acquired them.

I use at the moment:
bittrex.com
binance.com
coinbase.com

Binance being newer has some cool things going for it including its own Binance Coin (BNB) that if you use for fees they chop fees to 50%.

There are a ton of exchanges out there, but I personally use Bittrex and Binance.