Best investment (outside of investing in myself) was buying into Ethereum when they first announced it. In the 2-3 years since, that's been up nearly 50x.
I've only invested in two things outside of my 401k: Yahoo and Ethereum. Yahoo at $50, and Ethereum at $16. I am horrible at investing. I spent $200 on Yahoo and $40 on Ethereum, since I was just messing around, but damn do I feel discouraged.
Investing in spaces you don't know or don't have strong hunches is difficult. I'd recommend just putting money in index funds unless you feel really, really strongly about an investment and/or have some special knowledge of the space or company.
Though, in the long run, losing $250 while getting your feet wet in investing isn't that bad.