First of all technologies are good for career. Nothing is better or best.
They are made after pouring years of hard work from their inventors and they are made to serve definitive purpose in computer world. And they are doing their job pretty well in their fields.
Hence, people are hired for all of them and in demand all the time. Main thing is that which technology interests you, so that you can learn it with interest (with self motivation without being pushed) and since you like it, while doing your job it will give you work satisfaction along side of money. Something like what Computer profession is for Bill Gates, Cricket for Sachin Tendulkar and Films for Aamir Khan.
Still to help you choose the technology that is best for you I would like to precisely define their purpose and what type of jobs you get in that.
Oracle - It is Database software. A software program for storing, retrieving and manipulating large amount of complex data to present to user in useful way. So, if you love database concepts and can do great in this go ahead. Typical roles are DBA, PL/SQL programmers, Database Designers/Architects.
.NET - It is development platform (set of all tools/concepts to create a software) to create software that specifically target to run on Microsoft Windows OS. .NET is language independent (means write you code in any language C#.Net, VB.Net, VC++.Net all converts finally to same low level language called MSIL) so language is not a concern.Main thing is type of the software you want to target. There are only two types of software that can be developed in computer industry.
1. Desktop application / Windows Client Application - Example Microsoft Office. Windows Media Player etc. Main technology to develop these types of software now days is Windows Presentation Foundation (WPF) earlier was 'Windows Forms (WinForms). Jobs are C# developers with strong knowledge in OOPs, GUI Architectures like MVVM etc., Multithread application development.
2. Web Applications or Websites (Portals) - Example Google Search Engine, Hotmail, Gmail, Facebook. Main technology to develop these types of software are ASP.NET and Silverlight. Jobs are Web Programmers (Senior/Junior Level) using C#/VB and having good knowledge of OOPs.
For both types of software you can choose any language C#.Net, VB.Net even PHP.Net (see http://phalanger.codeplex.com/).
Hope these details provide some clarity while deciding to choose between Oracle, .NET and PHP. Best of luck for your career!