I choose bitcoin, if you want a long term investment then you should choose what's trend in our world today. Bitcoin is growing in every aspects with these past years, this is the reason why I choose bitcoin over gold. 
both investment is actually really good. gold is good for investment and the sole purpose of everyone make an investment of gold is for their future backup becuz they think making an investment into gold is a good idea since it's not moving so fast like in bitcoin so having both bitcoin and gold is fine and treat gold for your backup