[cmurf]

Retirement investments? The best option is do nothing.

Second best option the younger you are? Hope there's a big crash sooner than later. All you contributions from that point on, grow faster (from a discounted position) than any contributions made before that point. So the main strategy here, since hope really is not a strategy, is to make sure you're ready to invest as soon as the market does correct, and to invest as much as you can in the short term following that correction.

Anything else is a game that starts approximating gambling. e.g. go to a stronger cash position now with the plan to buy (in tranches) at perceived market lows. Basically sell when you're feeling confident, and buy when you're feeling nervous (following a crash). If you're selling when you're nervous, you're doing it wrong. Buy when others are selling.