The ISO 14001 Lead Implementer course has two parts: one with the foundations of the standard, and another about planning, implementing and controlling a management system implementation project.
The ISO 14001 Lead Auditor course has two parts: one with the foundations of the standard, and another about auditing. If you want to be Lead Auditor in your company, you have to fulfill the internal requirements for internal auditors. Normally, those requirements consider knowledge about the standard and good audit practices. For being internal auditor, I recommend the Internal Auditor course. The Lead Auditor is more for those that foresee working as external auditors, even working for a certification body in the near future.