Hello jyoti,
As far as your query is concerned , i completely agree with what fayiqa has stated here. What mostly we look for our system design is to work on least bit error rate and maximum quality factor pertaining to good overall performance of our system. So you should try to get it as small as possible which means higher negative raised to power term. In order words , e^-50 will give you better results than e^-12 or e^-10. I hope you find it helpful.
Regards