I've earned at least 75k gralats from Trialpay over the past two or so years...it's best to do them on PC, there are a lot more offers. For me, they have about an 85% success rate if I do all the steps correctly and fulfil all the requirements. If I don't get my gralats, but I know 100% that I've completed all the steps, I screenshot the proof and send it off to the Trialpay customer support which is located in the Trialpay GUI. I get my gralats a few hours later.
Surveys, downloading apps and playing games (only Facebook ones) are the best options. Never do ones that require you to pay money as that defeats the purpose of 'freebies'. You need to be patient and take your time, don't rush through things - it has multiple ways of picking up if your blitzing through things recklessly.