The best investment option involving Bitcoin is.... Bitcoin itself. Bitcoin was originally intended to be a currency. But nowadays, it is mostly behaving as an investment asset. And I would advice every one to stay out of the other Bitcoin-linked investment options, such as crypto-stocks. Most of these schemes are ponzis, run by conmen.
This, but OP is probably asking about some alternative besidesj ust holding BTC. Personally one of my favorite picks is Maidsafe. I love the philosophy, I love the project, and i love the already showcased technology. It's real and it's and it's happening. The testnet is already working. Amazing stuff. It's way better than Ethereum if you do your research.