RTC and MS Project are different types of tools.  However, you can use RTC to do task planning and track the progress of your project by completed tasks (as you can see on the product project pages here on jazz.net).

MS Project is designed as a planning tool.  It is not a source code version control system, or a build system, or many other things that RTC does.

RTC will not allow you to do resource levelling, full critical path analysis, and many other project management options that are mainly of interest to project managers, and normally not so important to development :-) 

If these project management things are important to you, then you should use MS Project.

If you want to track your actual progress as a development team (or a business analysis team, or a design team or a test team, etc) then RTC may be the right thing for you.  The most important part is that you get the tracking and updates to the project by performing the typical tasks of (for example) a developer.  Fix a defect and mark it completed, and the plan takes that into account automatically and updates a lot of information including the project progress and plan.