The important discussion where to use APEX and where to use ADF tends to get bogged down in an unproductive argument about the relative merits of PL/SQL or Java. However, this is not really the most important factor that should drive your decision.
Instead, you must first determine if your application is
- Data-driven, or
- User interface driven
A data-driven application is one where the data structure determines the user interface. Existing Oracle Forms applications tend to fall into this category, and if you only want to do a one-to-one replacement of a Forms application, the wizard-driven, browser-based approach of APEX works well.
A user interface driven application is one that starts from a set of requirements to support a work process. This is typically the case for new application development, or where an existing Oracle Forms application is being redesigned. User interface driven applications are typically specified with detailed screen designs that are easier to implement with the flexible architecture of ADF.
If you are in Norway for the OUGN spring conference, you can hear me talk on this topic in the presentation called “APEX or ADF? From Requirements to Tool Choice”.