This logic, "looks to be old," therefore the other is "better," is flawed. There are plenty of modules on CPAN which do exactly what they are meant to do and have not required patches and thus remain "old." Another word for this is "stable."

In this case, your invalid logic have lead you to the correct conclusion. So you're right in spite of yourself. Pg is a direct wrapper over the PostgreSQL C API. Recently, the PostgreSQL core team took over maintenance of DBD::Pg as well as Pg. They deprecated Pg in favor of DBD::Pg and it is the first and primary module you should use when interacting with PostgreSQL. The compatibility mode module DBD::PgPP was created by some other person and is useful if you can't use the standard DBD::Pg module.