If your work involves consideration for ROS and radicals like carbon monoxide and carbonate radical, then this may be the order of preference:

PBS >> HEPES > Tris

Tris is worst because it contains a rather reactive primary amine. 

PBS has virtually no target groups for ROS to attack. 

You can take a look at the methods section of this book (Part V, Chapter 32):

http://onlinelibrary.wiley.com/book/10.1002/9781444345988

thanks a lot....