I personally use Weighted Average in
Price Tracker Updated.
But you should be aware of Price Tracker limitations. Price Tracker uses prices from items listed in guild store, not from sold items. It means that prices could be atificially inflated by someone who lists items for absurdly high prices. Price displayed by
Shopkeeper is much more accurate, because it uses prices just from items which were actually sold. However Shopkeeper has a lot less data then Price Tracker, so there will be cases when you won't find price for item you want to sell.