This depends a lot on your personal situation and preferences, but after maxing out all tax advantaged options (401k, roth, HSA, etc.) I prefer to invest my remailing cash in my Vanguard taxable account.
This serves as an extra emergency fund that's always available penalty free, and the taxes on low dividend domestic stock funds aren't that bad until you need to sell, which will hopefully be after retirement when I'll pay 0% cap gains (unless Trump changes that).