I would prefer good service and reliability over best margin. What is your experience with CDF trading providers?
I managed to beat them in the 90s. Unfortunately I am no longer welcomed in any Casino worth to visit.
You will always find complaints with any broker you look at, Pepperstone has been good. It can't hurt to open demo accounts with a few to see what they are like.
Then obviously one should not trade CFD's whilst pissed, or without the basic knowledge of risk-management.