Namecoin does not hide server location, Tor .onion service does.

Namecoin does not hide visitor location, Tor does.

Namecoin needs separate DNS configuration, Tor .onion addresses works ouf-of-box, at least for Tor bundle.

Namecoin needs constant mining, Tor does not need.

Namecoin is secure from takeover, Tor .onion addresses also are secure.

Namecoin is interesting experiment and proof-of-concept, but there are better solutions. .onion FTW!