Just check on the trading sites where you want to trade, pretty sure different trading sites has slight price difference also.
Between the two, I use
http://preev.com just to monitor, it's not a heavy site, so it's suitable for my slow internet connection.
Well this is true that there are so many site that will give you different price graph but I think some of them are quite real. The site you share the link of is also know the present price values according to me I think we should follow all those who has market regurgitation. This could be safe as much as I know.