or you could just continue to let your sister run your life
Just joking....after you've thought about your situation and how your vehicle is used to support your life's activities, make your decision and go for it.
The G8 is a great car and while it's an automatic it is still fun to drive. If you don't need 4 doors, the camaro could be an excellent choice. Though it if you ever need to haul something large, and you don't own or have access to a truck/suv, you might be limited.
And please, don't be one of those idiots that I see all of the time who buy some "big-box item" and try to stuff it into your car outside of BestBuy or the lumberyard.
Best of luck....and tell your sister to mind her own business (unless she's paying for your car) then be nice to her!
Regardless, please buy American (and particularly GM) if at all possible and show your support for American manufacturering!!