The III obviously has significantly more processing power. We're all going to say the III sounds better as well, but that's always going to be somewhat subjective. Here's what I can tell you for sure....Every time I get a new guitar processor, the old one becomes my back-up, and the current back-up gets sold. I started with Fractal on the II XL+. I bought my first III in July of 2018. I did not take it on the road until April of 2019 (I was waiting on FC availability. I didn't want to have to program two different pedals). In November of 2019, I bought a second III and FC as a back-up rig because I felt is WAS that much better than the II. HOWEVER....I still have not sold the II. The quality is still there, and I still have enough use for it in my studio that it's worth keeping.