I disagree that only a limited amount of gold exists and that that's why it is protected from inflation. Who knows how many places which are still unexplored could contain gold. Cash is out of the question in that regard. So Bitcoin is the best like you said. 
Gold ofcourse does not have a limited amount, there can still be a lot of gold inside the earth or in the sea which are not discovered yet, while bitcoin has a limited amount because it is something that cannot be generated anymore nor there are any more bitcoins to be discovered.
I agree with this regarding on the amount of each which they do really differ hence a digital currency and a natural mineral can be found on earth do really have differences. Bitcoin is limited and gold is unlimited even they have differences they still have smilarities like increasing price and also a good investments.