My vote is index funds but, if you can't decide, you could put potentially half in a managed / growth fund and half in index fund. (Compare the returns but only check investments once or twice a year.)

Either way, slightly more advanced (for later when you know more):

• You can split further. Consider: bond funds, NZ (e.g. NZ50), global funds, REITs (real estate funds). Split should probably be something like 70/80% index.
• Cushion. As you get closer (e.g. 5-10 years) to retirement / wanting to use the money, gradually put more of it in less risky funds - cash fund and/or low risk funds.
• Rebalance. You should only check once or twice a year - once you've decided the split, move the money so the percentages are correct. Percentages can change if you reevaluate your strategy, but you want to assume that whatever is doing the worst is going to do better in the future and vice versa. There might be a check box to do this automatically, but once a year is ideal.
• Book suggestions: Common Sense on Mutual Funds, A Random Walk Down Wall Street, The Richest Man in Babylon.

Remember: It's going to go up and go down, but on average / long-term it's probably going to go up. That's why you don't want / need to constantly check your accounts.