Should I buy an 09 or 2010 RT?

Huh? Not much difference that I know of, other than one is a year older than the other. Comes down to finding the car you want at the price you can afford.

I guess the other obvious is almost all the '09's will be used; there's still a lot of 2010's out there new.

more color options in 10

If the 09 is new it will come with a life time power train warranty.