I see. But which one is technically graphically better?
I've went a bit down this particular rabbit hole. Not with dreamcast in particular, but with video options in general. My advice? Stop now before you invest too much time and effort.
Stop worrying about what's "technically superior" and worry about what
you think looks best. In the end, that's all that matters. Because if you start worrying about getting the best output, you're going to find yourself at the point where you're either trying to track down old medical or broadcast CRTs, or you're buying upscalers that are over $300 (and sometimes you use multiple) and monkeying with settings, cords, homebuilt adapters, SLGs, etc etc.... it's too much.
Stop worrying about what is supposedly better, and go with what you think looks best. That's my advice at least, take it for what it's worth.