Aside from startup investing, where would you allocate $500k? Real estate? S&P? Gold? Cash? Bitcoin? Assume no diversification - you can only put it in one place.
It is a stupid question, though, as it makes no accounting for your individual situation, an important thing that defines your relationship with money.
S&P through a low fee mutual fund or ETF. It is boring but over the long haul will probably have the best performance.
If I was placing an all or nothing bet with $5k it would go in bit coin. I doubt the volatility will go away anytime soon so I suspect that it will either continue the explosive growth or crash.
The assumption is stupid. Sorry to say that, but it is.
If it is throwaway money, put it in bitcoin. It definitely has the greatest potential to double in reasonable time. It also has a fair chance of completely crashing, but, hey, it's throwaway money.
https://personal.vanguard.com/us/funds/snapshot?FundId=1487&...
(Actually, I have more my ~$300k in other Vanguard funds, but if I had to consolidate to exactly one, that'd be it.)
You could also make a case for VT (Vanguard Total World Stock ETF).
https://personal.vanguard.com/us/funds/snapshot?FundId=3141&...
It is a stupid question, though, as it makes no accounting for your individual situation, an important thing that defines your relationship with money.