Depends a lot of your situation. Age, family (wife, child etc), job security and pension plan. How did you react with your investment in 2008 ?
Ex. 1- You're 30, save +/-50% of income, no child, safe job, went thru 2008 without selling (stock), I would rock on 100% VBR (small cap value) for the next 10 years at leat then review my A.A.
Ex. 2- You're 40+, +/- safe job, no pension plan, new to investing (less than 5 years) so 2008 did't hurt your savings...then I would bet on 50-60% VTI, 20-30%VXUS and 20-30%BND.
Hope this help !