I have one(05GT), wife has the other(RT charger), father has 300c hemi heritage edition.
If you want to build a fast car. Go with the GT, just soo many more part vendors, blowers, turbo's, engine builders, and great groups around the country.
If you want to be cruising in comfort, need the extra doors and space, don't mind the extra 1000lbs, the lack of a manual tranny, yet still want a fairly quick car with some balls on the highway. Get the Charget RT with R/T package. Hell or better yet the 300c hemi heritage, more cash but just as fast and way more plush on the inside.