According to me, the title is not correct. "What dhikr have you used and benefited the most from?" This all depend on one's Yaqeen(trust) on how he/she is doing. Whatever our prophet said each and everything is beneficial. Testing it is against his imaan on his beloved his imaan. We should have such yakeen that if our prophet said then it will happen that's it whatever will be the situation. Sahaba has not tested. They do have such yakeen that they have ran on water along with their horses. Everyone keep posting your views but for Allah's sake stop telling your testing methods.