if i had to pick between the challenger RT and the camaro V6 I would hands down go with the Challenger RT. if i had to pick between the SS and RT i would pick the SS.
the SS will be faster and handle better than both the v6 camaro and RT Challenger.
the RT will be faster than the v6.
the v6 will get the best gas mileage.
the RT is the roomiest out of all 3 and still have some get-up-and-go.
all in all it depends on your taste. if its speed and handling the SS will be the one. if its roomy-ness and still have some get-up-and-go then go for the Challenger RT, if you want a slick looking car that will get good gas mileage then get the V6 camaro.
good luck!