I like to overweight Health Care in the hope it could be a partial hedge against my health care costs. HC will likely become a disproportionately large part of my spending, and is a high-risk expense for me, being on individual health insurance policies.
Speculatively, I don't know if I prefer US (or global) HC, over other US (or global) Largecap Growth, though I did when I last added to VGHCX. It has outperformed my portfolio though, since then. And, I believe, has outperformed VUG since I bought that, fairly recently--though VUG is US only (large growth).
If I were picking sectors, I might underweight energy today. Haven't run the numbers, but suspect it's pricey. I prefer commodity futures (PCRIX) in my portfolio, for their historically low correlation to stocks, and potentially good returns compared to bonds.