Just having an ample amount of bitcoins is already an investment, because bitcoin's price just keeps on increasing. You don't need to invest them in any other sites or hyip thing, most of them are scams and you risk losing instead of earning.

I use copay and mycelium apps to store my bitcoins, but i only store a few... those i use because as you know, it's always risky to store bitcoins in any online wallet. I keep most of my coins in paper wallets, those i plan to hold for the next five years.