FOP is for sure the harder of the two to get. You can reasonably expect to grab NRJ for a 4th or even 5th FP while you are there, or just ride it standby when the park opens.
I will go on the record now as saying that NRJ is much better, at least in my opinion, than most make it out to be. It was never meant to be an "E" ticket ride. It is not intended to be thrilling, or exciting, or a headliner. Instead, it was meant to be the modern equivalent of Small World. It is peaceful, and relaxing, and gorgeous, and in it's own way, every bit as enjoyable as FOP, or EE. So, if you are capable of riding Small World, or Living with the Land, or Gran Fiesta Tour, and enjoying them for what they are, then by all means, go enjoy NRJ.