Answer:
Firstly, you have to differentiate between interest rates and growth because they are entirely different things.

Interest rates are given by banks if you invest your money in one of their savings products. The interest rates quoted for fixed deposit are guaranteed for the period that you committed to. Other interest rates are linked to whatever the prime lending rate is at the time which is determined by the reserve bank.

If you invest your money with a bank in a traditional savings product, there is no risk of losing your money (unless the bank goes insolvent which is highly unlikely as banks are watched very closely by the regulatory authorities). But low risk usually means lower returns.

Growth, on the other hand, is linked to the growth of the investment that your money is invested in. If you invest in a unit trust, the fund managers that manage the unit trust will invest your money into various asset classes such as shares, property, cash or even gold. All of these investments are volatile depending on the state of the economy, the management of the companies and the rand/dollar exchange rate.

The amount of risk varies but as a general rule of thumb, the younger you are, the more (calculated) risk you can take with your investment strategy.

So to answer your question, I will have to break it up. If you only want to invest for the short term (two years), then investing in a medium to long term vehicle like a unit trust is not a good idea, because it may be in a downswing at the time you need the money. They usually show growth over three to five years. If you intend to access the money in two years or less, a bank product is your best bet (interest bearing).

Contact your bank and others to find the products that will give you the best returns. For a three to five year investment your best bet is a unit trust. Speak to a financial advisor about a medium equity balanced fund. This will give you the best return without high risk. There are many to chose from so a expert is definitely required to help you make the right choice.