I've tested nearly 10-20 common ones in the past few months, but what I've realized about growth hacking in general (other than the fact that the phrase itself is rather misleading) is that it should be a lot less about techniques and more around a mindset. You can significantly hurt your business if you just try things others have tried and gain traction that just isn't real and sustainable. I think that's why no one has really answered your question here for a few days to begin with.

Good luck! More than happy to chat about the specific tests I've ran in the past if you're still interested.