none, you aren't using gpu, just whatever cpu is the fastest. if you want gpu acceleration you have to specify it. and keep note gpu acceleration is less efficient then cpu so your files will be bigger. though at preset fast it might actually be pretty close
Yes this is indeed what I said. but well calling gpu encoders "worse" isnt really fair, it's all trade offs, they for sure have worse efficiency as we both said, but their speed is significantly faster usually. I would say that doesn't make the encoder "worse" just different.
Better quality:Compression ratio you can easily get better quality out of a gpu then a cpu depending on your settings, but it will rarely be better quality AND compression unless you have a quite slow CPU and cant run a sensible preset