This question really depends on the source location of the gold and diamond that you consider. If you're looking to mine them out of the earth's crust, gold is often a lot more easy to come by than diamond. However, nowadays, diamonds are relatively easy to create as diamonds is an allotrope of carbon formed at very high pressures which can be simulated in laboratories, carbon is extremely abundant in the Earth's crust and therefore it is relatively easy to create diamonds. Gold on the other hand is a siderophile element and therefore partitioned into the earth's core during the early stages of planetary differentiation.
In the bulk silicate earth (this includes the earth's mantle and crust) diamonds are probably a lot more common than gold. A lot of diamond probably resides in the hydrated mantle transition zone and is brought to the surface by kimberlite pipes.
In the earth's core however, it's probable that large amounts of gold reside, and so in this reservoir gold is much much more common than the lithophile carbon. I've heard the statistic that you could coat the earth with a layer of gold from the core to a depth of half a meter but I'm not sure how true that is. Even so, with all the gold in the core, the amount of diamond on may well be higher as the bulk silicate earth is a much larger reservoir.
In the universe as a whole, carbon is much easier to form as it can be created through the triple alpha process, whereas gold needs to be formed either through the r- or s-process which occur in supernovae and asymptotic giant branch stars respectively. As such we can say that most planetary bodies contain more carbon than gold and therefore diamond is more abundant in the universe than gold.
I hope that this clears up your question YouCannotHide