in my opinion best way of earning bitcoin is to do online jobs and get paid with bitcoin. another good way is trading but only if you can and don't lose money doing it.
Work for bitcoin is the best way i think, because "earning" means you don't need risk anything, just spend your time for "earning" itself.
Trading, if you good in trading is other best way too, i see people get a lot profit with trading but you need to learn first.
if i can enrolled with other sig campaign, maybe i will think again 
, but of course I try to make some extra BTC without paying for it. For the last two weeks I visited freebitco.in, moonbitco.in and the zebra faucet on a regular basis. Got some Sathosi from that which are worth 1,76 $. That`s a really bad hourly wage. But I have to say that there are no refferals in this amount.