Take a look at this thread as everyone has different opinions on which one is better. http://forums.afterdawn.com/thread_view.cfm/152082
they both have 30day trials so try them both and see for your self which one fits your needs. I would recommend trying before buying.
I have just installed panda and by the looks of things the search stops here. This is a great program and it has found stuff that norton didnt even smell.