I know very little about the middleware from a programming perspective. I install and configure the WebLogic infrastructure, but I don't get involved in any of the development.
Regarding which way you should go, I would not at all be considering Oracle Forms as a career choice these days. Oracle still support Oracle Forms because it has a large number of customers and supporting it keeps generating revenue for Oracle. Having said that, I know very few companies that are actively developing new applications in Oracle Forms. Most are just maintaining existing applications, while new applications are developed in something else. In some cases, the new stuff is done using ADF, but not always. Making a choice to learn this skill set now is investing time and money in a dying skill.
The thing to remember is, front end programming, like web interfaces, if kind-of separate the the back end stuff. I only work on the back end stuff, like databases and application servers. We have applications written in Forms, ADF, PHP, .NET, VB, Access and they all speak to the database, so I don't really care what people develop in, so long as they use the database properly.
If you speak to a developer, they may have a very different take on things to me.