I get reasonably good results photographing negatives with a slide copier attachment and a macro lens (vs using a flatbed scanner). However, if you plan to scan many frames of film, you should consider a dedicated film scanner with batch feeder. Depending on your lens and camera, image quality from a film scanner may or may not be better, but it would be much more convenient.

Flatbed (or film) scanner

Advantages:

• Scanning negatives is an anticipated use case. Software usually include ability to invert and color correct negatives, often with single click.
• Scanner may have automated dust removal features (via additional infrared channel).
• No demosaicing.
• When image doesn't turn out well, it's most likely a problem with the film. (Don't have to constantly second guess scanner and settings.)
• Light source is built into the scanner. Results are consistent.

Disadvantages:

• Capture process can be slow. Scanning is done line-by-line.
• Focus and resolution of some scanners may not be optimal.
• Scanner takes up desk space.
• Scanner likely cannot extract "all" information from film (grain structure and dynamic range).
• Software usually automatically crops frame. May have difficulty capturing sprocket hole images. (More problem with film scanners than flatbeds.)

Other:

• Convenience, if using a film scanner with an automated feeder.
• Flatbed with transparency adapter is best (and most affordable) option for medium format.

Digital camera with slide copier

Advantages:

• Capture is fast (about the same as taking a picture).
• With good macro lens, can focus on image grain.
• With increased magnification ratio, can extract more information from image (grain and dynamic range).
• No scanner to occupy desk space.
• Reasonably affordable if you already own the camera and lens. (Slide copier attachments are ~$35-50.)
• Depending on attachment, can capture images that extend into sprocket holes.

Disadvantages:

• More time is spent post-processing images.
• Have to demosaic. Reduces resolution and may introduce artifacts.
• No automated dust removal.
• Photographing negatives is not a normal use case.
  • Camera may not meter properly.
  • White balance won't work properly.
  • Software is not designed to invert and color correct negatives. May have to spend lots of time tweaking curves.
  • When image doesn't turn out well, is it a problem with the film or camera or software? (Constantly have to second guess whether camera or software is at fault.)
• Focusing on grain can be difficult (depending on lens, magnification, and eyesight).

Other:

• Need to purchase a slide copier attachment.
• May need to purchase a suitable lens.
• Aberrations and distortions depend on lens.

• Contrast, sharpness, dynamic range depend on lens.

• For best results, have to use reproduction ratio greater than 1:1 and stitch.

• Depending on how careful you are, lighting may not be consistent across the frame.

• Medium format...

  • Difficult to find suitable slide copiers.
  • If using a lightbox, will likely have alignment problems.
  • Will likely have to stitch several images.