For most project managers the best route is APMP from the APM.  PRINCE2 is essentially a methodology whereas APMP is a body of knowledge including skills and techniques.  So whereas PRINCE2 training will indicate when to estimate and when  to produce a schedule, the APMP course will show you how  to produce estimates using a variety of techniques and how  to schedule effectively. If you want to be a well rounded project manager then APMP training is an obvious next step qualification and a great compliment to the PRINCE2 Practitioner qualification.  The APMP for PRINCE2 Practitioner training course is the best route as it builds directly on the knowledge gained in PRINCE2.

There are also other project methods to investigate such as Agile and Scrum training, which is ideal if you are working in a fast paced development environment.  Agile and Scrum is popular in software development but increasingly is used across IT and other projects.  Having the skills to run Agile projects is complimentary to PRINCE2 so you can look at the right methodology for the project.

PRINCE2 Agile is a complete project management solution that combines the flexibility and responsiveness of Agile with the clearly defined framework of PRINCE2®.

Programme and portfolio management is an option, especially if you work in a larger organisation that runs projects under the umbrella of programmes and wider business change initiatives.  The most widely used methodology for programme management is MSP (Managing Successful Programmes).  Training and certification follows a similar route to PRINCE2, with MSP Foundation followed by MSP Practitioner training.  MoP (Management of Portfolios) also has a Foundation and Practitioner level certification.

Finally P3O (Portfolio, Programme and Project Offices) Foundation and Practitioner is a good choice if there is a desire in your organisation to create a support office to assist PRINCE2 project and MSP programme managers.