Both were great but Giuliani had to clean up a far bigger mess so I would say Giuliani was better.
lol crime began decreasing under Dinkins, not Giuliani. It was Dinkins, not Giuliani, who cleaned up Times Square and began broken windows policing, but Giuliani still slandered him as a weak-on-crime thug because of the color of his skin. Dinkins was not some sort of far-left commie like many portray him to be, he literally endorsed Bloomberg in the 2020 Democratic primaries.
Giuliani literally did nothing as mayor except say racist things. The drop in crime was caused by Dinkins-era policies and the removal of lead additives from motor fuel. Bloomberg raised taxes, implemented the largest affordable housing plan, created bike lanes and pedestrian plazas, liberalized immigration laws and prevented thousands and thousands of immigrants and refugees from being deported, banned trans fat and indoor smoking, policies which have saved millions of lives around the world, signed of the first trans-gendered rights bills in 2002, fought for congestion pricing, started 311, etc.
Meanwhile, sort of like Trump, the only thing Giuliani did in office was say racist things.