I think the best invest site will be Betking.Io...why?
You can check here at Dicesites.com.Their profit is better than any other bitcoin dice site who have invest option.Or you could convert your bitcoin to XMR and invest on Safedice.
most of the investment gambling sites are the same, especially the top 10 because as long as they have players playing there you can count on getting profit.
and in case of betking the high profit you see now is because of a one time big lose of a big whale.
If you worry about the whales can win big amount then the best solution is to diversify your funds and put in many good sites then you can reduce this kind of risks. Because big wins will not happen on all sites at a same time and in the longer run, you will be in profits.