From what I have gathered, here and elsewhere, ECM Spy is easier to use, but Tuner Pro is a lot more powerful, it gives you complete control over every aspect of the ECM, if the ECM controls something, you have control over what it does, I am by no means an expert, I have yet to do any tuning with either of them, but when my EBR ECM comes in, I will start learning Tuner Pro, on my stock ECM