Yeah I use both, interesting that you have noticed. These days I rely more on coinmarketcap, where prices are in USD:
In the past I used Poloniex mostly.
But I keep track of both, as a benchmark for my assets. In fact I am also working on a theory where I can determine my absolute wealth, since as we know all markets are relative (EUR/USD , USD/JPY, EUR/JPY)
It is possible to triangulate an absolute value from fiat currencies in enough pairs are used, I am exploring this idea.