A sort of natural experiment happened to my investments in the last decade. My 401K was all bond fixed income portfolia, with steady monthly contributions $CA. I had one mutual fund account, 4 all-stock-index funds. Steady monthly investments $CA. My 529 plan was a "age based auto rebalancing" monthly contribution plan $CA. And I had one "actively" managed account, no $CA, market timing, driven my astute analysis of the market conditions and market timed trading done by a brain proved to be in the 99th percentile. What with JEE-AIR(*) 800, GRE (790v, 790a, 800q) and not!
Well, the age based rebalancing 529 plan survived the crisis best, never went below the cost basis, and produced very reliable and steady gains. Averaged over 9% for 2005 to 2014.. The bond 401K net value dipped below the invested money for a brief period, 3 months in 2009 Feb-Apr 6% annualized return over 2005-14. The stock mutual fund went below cost basis most of 2009, but it too came roaring back, 7% annualized same period.
What about the super brain actively managed portfolio? It is the dog. 4% for that period. If you remove the 2% inflation component out, 529 did three times better than active management, even the bond fund was twice as good, the stock fund is 2.5 times better than active investment.
So, folks, the moral of the story is, go for dollar cost averaging, and do regular rebalancing. I was very fortunate I did not have to liquidate any of my portfolio in the middle of the crisis, that is what saved my tail. Not my active investment. Simple brain-dead $CA and the luck of not having to sell anything during the crisis.