The Bible is the only thing to preach 1 Corinthians 1:21
Yes, the things of God are foolish to those who don't believe, so just quoting the Bible to an atheist is just going to make his react as if what you are saying is just foolish. I just wonder, if you actually do witness to atheists, if that is the reason you don't get anywhere with them.
I have watched a number of Ray Comfort's witnessing to atheists on his Living Waters Youtube channel. He shows real success in getting through to them, and there are times when he has convinced an atheist to actually believe that God exists, and has led atheists to the Lord.
It would be good to see how he goes about it. I wish I knew when as a younger person in a coffee bar ministry witnessing to guys who didn't believe the Bible.
In fact, all Ray is doing is doing what Jesus did when He spoke to people. He did not say that one who believes in the gospel will just have a happy life. Often He said that suffering and persecution will more likely come when a person believes. He also challenged people according to their compliance with the Ten Commandments and showed people that they were sinners in their hearts and needed a better righteousness than the Pharisees.
So you will see that he starts often with asking people if they are good, and then shows them they are not good, and they are in danger of the judgment when they die.
But watch it for yourself, and it may revolutionise your thinking about witnessing as it has done for me.