Monetary-wise bitcoin's already surpassed gold.
Longevity speaking though, that is a little hard to discern. Gold's been the standard of money ever since we learned how to count. It has value that we have already agreed upon and while it doesn't rise as fast as bitcoin, it's on a steady increase as the supply here on Earth dwindles. A case could be made for mining precious metals on nearby asteroids or whatever but that's a farfetched tale the way things are looking right now, and besides, it's not as if that will immediately dilute the value of gold anyway.
Bitcoin however, while fairly valued, is a little volatile for most people's tastes. This could deter them from investing, and not to mention the immutable supply which will only make it harder to get a hold of a bitcoin in the future.
volatility of bitcoin will significantly be reduced once BTC is approved for strategic bitcoin reserve and then big corporation and institutional investor will put their money, which mostly made up of passive investor, who just holds, into bitcoin and as a result lesser supply in the market and greater stability of price.
although you say asteroid mining is farfetched tale, I don't think it's that far from happening, technology advancement happen at really fast rate, see the technology 100 year ago and compare it to now, then you'll realize maybe in just 30 year we already have the technology for asteroid mining.
Gold was a good investment before couple of years but we saw a huge pump in the gold market and now gold is very away from middle class people. Soudi Arabia is making their own currency,so they took gold of billion of dollars,So gold price is all time high . That is not best time to invest in gold because gold price will go down after few months . Many investors got profit who invented in that before 2 to 3 years. Now that is time to analyze the market because bubble will make then we will see gold at low price,that will be best time to buy the gold. But now that is best time to sell the gold stocks if you have because market situation will change.Due to Saudi government effect ,gold price is going up and up and we will see huge pump in that in couple of months.