Gold coins.
Gold coins are ideal for both small and large investors.
Gold coins allow flexibility as you can buy small amounts over time to build wealth gradually.
For UK resident investors coins such as Britannia coins and British Sovereign are especially popular due to being Capital Gains Tax (CGT) exempt.
Gold bars.
Gold bars (in large quantity) can be subject to Capital Gains Tax in the UK and can also be potentially harder to sell or store.
Gold bars do have some advantages of economy of scale whereby the premium paid over spot price could be reduced the bigger the gold bullion bar.