I am about to take the LFCE, CentOS 6 or 7?

So I bought the certification exam on 02.12.2014, and I am about to schedule to take it mid-November for the first time. One retake is free if I fail for some reason.

I've been dealing mostly with CentOS for the past 4 years, prepping VM templates on CentOS 5, then dealing mostly with CentOS 6, but CentOS 7 had its fair share of issues so it wasn't the most used on our infra, so I didn't get much exposure on it.

Because I chose CentOS 6 while it was still available, I see that I can still schedule to take the LFCE exam on CentOS 6.

What do you guys think? Should I do it on CentOS 6, or switch to CentOS 7? I guess CentOS 7 is the way to go, as it's the latest distro, but I feel safer doing the CentOS 6 exam.

Any experience from guys who have done the RHCE/LFCE 6 and 7 would be greatly appreciated.