As regard to the best way to earn, i think completing tasks are much more better than the ptc clicks.
I have to agree with that. I like the crowdflower tasks a lot because they don't ask for any personal info or stuff (like lot's of the surveys do, let alone all the sweepstakes that want to be fed email adresses or need you to subscribe to some mobile app provider). The downside though is they take some more effort and time. But I'm fine with that. This evening I'll start a test with the Answer question tasks, to see if it is worth the effort to put together good quality answers.
With the current offer/task contest, you could win 0.50BTC, the highest of the available prizes.