Before we examine what is better investment gold coins or gold bars, we must remember one thing. Any type of precious metal bullion is a better investment than paper currency.
Gold bars are suited to the serious, large scale investor who wants a simple and 
efficient way to invest in gold. The larger bars are always available at the lowest premiums over their intrinsic gold value, smaller bars tend to cost substantially more.
On the other side, it is difficult to sell a 1-kilo gold bar as most investors are not familiar with gold bars, and you will need to find a larger dealer, as finding a private buyer is going to be a difficult task.
Gold coins is the type of investment suited to the smaller investor. I personally prefer to invest in an ounce gold bullion coin, rather than an ounce gold bullion bar, as coins are massively produced and can be purchased at very competitive prices, compared to gold bullion bars.
The quality of gold coins is also guaranteed by the government, rather than a private 
refinery. At the same time, coins are very easy to resell. Many investors, only examine the premium price, (the percentage over and above the current gold value at which an item trades) when they buy gold, but do not realize that coins can have a premium at the time of sale, which is can be beneficial to the seller. A premium price can vary from 1% to 10% or even more.
Older coins, such as the British sovereign carry a higher premium, rather than a modern coin such as the Krugerrand. At the same time a large-scale investor, who will actually invest in a large number of coins will actually pay a small premium.
My recommendation for the large scale investor is to invest in gold bullion bars, as 
bullion bars is the most efficient way to invest in gold. Bare in mind, I am not talking about a 1-ounce gold investment but I am talking about a 1-kilo investment.
A smaller investor is better off investing in gold bullion coins, preferably older coins such as the British sovereign, as the sovereign carries a high premium. In addition, coins are easy to resell.