Both can be profitable, but if you do bounty, it depends on your bounty project, because not all bounties will pay you 100% sure, some bounties are fake. And some bounty projects will pay you less money than you expect, and the bounty projects that are very good will pay you much more money than you expect. Like you can get $1500-$2000 if you work on a good bounty project (Only in terms of understanding). It totally depends on the project.
Now if you invest in bitcoin or other good coin or any other good place for long time, it will definitely pay you well, because long term investment has much less risk. The longer you hold here, the higher the return potential.
Invest or bounty both things are best, both give us high money potential, now it's up to you to decide which one you do, it's a personal matter. But in my case both are best.