I don't think there is one site that is considered most accurate since Bitcoin doesn't have an official price. The best advice might be to look at a major exchange that has good trade volume. If the trading volume is pretty high then Bitcoin shouldn't have any abnormalities in price and should be about the same price as all other major exchanges. Some of the major ones are Bittrex, Bitfinex, Kraken, and Poloniex. You could also look a the price at Coinbase but they may inflate their price for profit since their exchange is a little different.