there is kinda a rule for certain lil luxury/life purchases...
like sail boats, RV's, planes, generally get one larger than you think you want.
like woodsplitters, saws, tow vehicles, get one with more power than you think you need.
like motorcycles, houses, camping tents, buy the one you will grow into, not the one you will grow out of.
The R/T is going to get you a seat at the entry level muscle car table.
The GT's & SXTs are very nice, for a V6, they are more than capable, but they are not viewed nor perform the same as a 375hp rear wheel drive car with a ton of aftermarket support, simply because they are not targeted to the same buyer.
What I have noticed is, each trim level attracts a certain type of buyer. Its not a bad thing, I love all challengers, but when you see guys trading in 1 trim model for the next trim level up, its a sign they didnt stop and get/wait to afford the trim level/options/model they really wanted in the beginning.
Having said this..if your desire is a muscle/perf car, than buy the most you can affoard, be that an R/T, scat pack, a fully loaded SRT, or what have you. other than payment cringe, Ive never heard a car owner, complaining his/her car had too many nice, warm & fuzzy options to enjoy.
If its a commuter with tons of style, lower insurance rates (< at your age , this maybe the biggest factor in your buying decision), better safety, less prone to tickets, theft, etc.. the SXT or GT line up is a sure win.
Good luck with whatever path you take.