For photographing 2D artwork, a true macro prime is the better choice. The Sigma 70-300mm “macro” zoom was described as soft, especially at the long end, with lower contrast and some chromatic aberration. It also isn’t a true macro design in the usual sense; lenses like this typically offer only close-focusing or about 1:2 magnification, not the stronger reproduction and optical performance expected from a dedicated macro lens.

A real macro prime around 50–60mm is the safer recommendation for artwork reproduction because these lenses are generally much sharper and better corrected. In the answers, the Canon EF-S 60mm f/2.8 Macro was specifically recommended, and similar true macro primes from Canon, Tamron, Sigma, or Tokina were also noted as optically strong.

If your goal is accurate, flat copy work, prioritize sharpness, evenness, and low distortion over zoom range. A dedicated 50–60mm macro is the best fit here.