I drove the ST hard at the Performance Academy Ford offered this summer, that car is awesome! I've driven the RT Dart at the dealer I work at, and it's not an even comparison. The 1'4/1.6l turbocharged engines sound cool and have more power than you'd expect from the diminutive engines, but if you're set on getting an ear-to-ear grin from a mash on the accelerator you want to wait for the 2.4l turbocharged SRT Dart. That uses the Tigershark 2.4l and upgrades a number of features and power ratings over the smaller choices. The 2.0l is available now, but I don't think that setup is boosted.
The VeeDub is going to be the high-line choice in this comparison. That car has a level of refinement not equaled by the other two (and a price to match!). It's that better lineage and parts bin.
I'm biased for Ford though; I'd rather have the ST!
"I'm gonna sing the doom song..."