If you manage a portfolio it's absolutely routine to ask yourself a question "what's the best thing to invest in right now?"
Even if you don't have a portfolio, it would be smart to ask yourself: "what's worth to invest in?" .....Obviously your prerogative is you want to build a fortune. Being this the case I remind you "a great fortune always begins with a small investment".
Much has been said about it, so what's worth investing in?
Results are the only thing that matters, as long as it's legal and ethical. Some investment opportunity may look sexy, but afterwards they come out as being hardly manageable and at the end of the day not very profitable. If you don't know what you are investing in, don't invest because you are at risk of getting burned.
My suggestion is to invest in something simple that pays you back with a stable cash flow.