A diversified portfolio of index funds. This year return so far is ~15% (which in absolute amounts is more than my after-tax salary, even after accounting for long term capital gains), and my annualized return since when I started investing (~a decade ago) is ~10%.
Which index funds do you like? I've been going back and forth between considering one or more index funds or just getting a target date fund and leaving it alone altogether.
That way, I can tune allocations if needed and I can take advantage of tax loss harvesting opportunities, so I get some extra benefits.