This would be a difficult question to answer objectively.
We would think that Christians would be likely to be law-abiding because they presumably have a moral code by which they try to live. But it would still be hard to actually verify this.
First, we would have to define who is and is not Christian. We would have to ask if anyone who believes in Jesus is a Christian. We would have to ask if someone has to have actually been “saved” to be a Christian. Or would it be based on how often they go to church?
Then, we would have to be sure that our sample of Christians (however defined) was similar to the “others” that we were studying. It would not do to take a sample of middle-class Christians and then compare them to poor “others.” It would not do to take a sample of rural Christians and compare them to urban “others.” This would make it impossible for us to know whether religion or some other factor was causing any difference that we observed.
Therefore, it would be very hard to actually determine if Christians are more law-abiding than people of other faiths or of no faith.