Anything other than signature campaigns and gambling.
A bit saved is a bit earned. So save your money by not clicking on any of the signatures of the people posting in this thread.
For me, the greatest way to make bitcoin would always be mining, because the earnings in mining is enormous. Although, the only problem I see with it is the fact that it takes money to maintain a mining system, not to mention the expenses paid for the electricity bill every month. Still, it is really and definitely worth it.