There are certainly pros and cons to both setups. Some of these are listed in [Support Guide] Should I use Netlify to manage my DNS?
A con for Netlify DNS is the lack of support for DNSSEC (see DNSSEC support on Netlify and DNSSEC on Netlify)
A con for using external DNS is the lack of AAAA record support for apex domains (see AAAA (IPv6) record for apex domains? )
If you are undertaking design work and not managing the domain for the client, I suggest using external DNS configuration. If you are managing the domain as well then whichever suits you best.