I'm thankful at least that you want to be a good person; not all atheists have been this way. For example, have you ever faced honestly the evils that were done in the name of atheism just in the last century (in Russia or China, for example)?
But I reject your claim that Christians do good because they're afraid God will punish them if they don't. This suggests to me that you've only studied Christianity from a distance -- that is, that you've never had any close friends who were Christians, or that you've never worked alongside any Christians in a homeless shelter or after-school tutoring program (to take two examples at random).
If you had, you couldn't help but conclude that they were acting out of love, not fear. The Bible says, "For Christ's love compels us. ... that those who live should no longer live for themselves but for him who died for them and was raised again" (2 Corinthians 5:14-15).
The greatest truth anyone will ever know is that God not only exists, but that He loves us and wants to come into our lives and change us. And this can happen to you, as you face honestly who Jesus is and what He can do in your life. Don't go through life with a closed mind. Instead, I challenge you to ask God to show you not only if He exists, but also if Jesus is worthy of your commitment.