why not both of them ? i think with saving 20-30% your profit/money to gold always be a good choice, they already have their own market that can'be ruined by any other thing, even bitcoin i think. Old people and traditional people that can't use technology still hard to believe bitcoin is really exist, but who knows ? we are the next generation of old people, we can teach the next generation 
I think a good idea by investing in both? Why not? If you have a lot of money you can share your money or the profits you get by investing in both. After all if the price of both goes up of course it can give double benefit to you rirght ?It is not about gold or bitcoin. Its about the percentage of money in terms of traded volume. The more the volume the more that asset will give you ROI. So how does the volume is decided? It can be from hours to months for particular market. On one side gold works for 5 days while bitcoin keeps working whole without a rest. This might be a fatal difference between the two commodities. Im sure bitcoin will overcome gold at any given time but who knows for how long the blockchain technology will sustain its root in the digital world. The fall and rise can occur at any time and the investment must be done with complete acknowledgment of these assets, questions like what is trade volume, how long the commodity is going to stay, how much involvement is there, must be asked every time you do it.