Gold ETF is purchasing Gold in Demat Gold Bar Format. This in my view has the biggest advantage that one does not get the delivery of the physical Gold, hence no problem of securing your purchased Gold. Also Gold could be purchased in small units. One could hold his gold in demat account till he desires. There is only a small maintenance and brokerage charges on the Demat account, so this in my view is the easiest and cheapest form of purchasing Gold. Also one could sold his gold anytime at the market price of that particular moment. So there are no deductions and one gets almost the full value for his money while selling it.
These days there are a number of Gold Funds or MF's where one can invest. These bonds invest the money only in the bullion market and are managed by Professional Experts. So if one do not have time or expertise to deal directly with the fluctuations of the gold market he could still invest via these bonds. However most of these bonds have entry and/or exit fees and have a certain lock in period. So this form of investment is mostly a long period investment. Another advantage is that these funds gives the ease to invest via SIP's. So one could invest in Gold in small amounts over a long period of time.