It really depends on what you are looking for in a car. The ST is a better car than the current GTI. As a owner of a GTI, I fully admit that. However, if aftermarket support and customization are important to you, the GTI is a much better vehicle, at least right now. ECS Tuning, APR, and some other companies offer so many upgrades and tuning options.
The Dart R/T can't even be mentioned in the same sentence. Its not a hatchback, it isn't out yet (Originally supposed to be August), and its chasis and engine are sub-par compared to the other two.
The only thing that irriates me about the ST, and the Titanium as well, is the lack of standard HIDs. The GTI and top Golf trims both have these standard. You can even get HIDs on a Fusion SE.