Good and bad are inherently subjective. There are objective features of things, but ascribing good or bad to them is a subjective association.
My opinion is the prequels are bad for technical reasons. I think they're just badly written and acted, the plot is incoherent and contrived, the dialogue is terrible, Anakin and Padme's romance is awkward and his fall to the dark side is unconvincing.
And as far as the new movies go, I think they (and The Force Awakens definitely) suffer (as did the prequels) from the need to shoehorn in references to OT characters just for the sake of pandering to fan nostalgia, but they still seem like competently structured movies.
Between the two, I think the post Disney movies are better because they better tell the stories they intend to.
Reasonable people can disagree, but I'll take subjectively bad over objectively bad any day. And I happen to be a bit of a fan of deconstructionist narratives, anyway.