I think the firebird and the camaro had some good model years, and some pretty lame ones w/peak muscle car performance comming in 1969. Anything you could order for one you could probably get for the other.
The '69 Firebird would be my first pick. There was one year when I would have picked a camaro, I think it was '70 somthing when the camaro had that big open grill, and the two piece front bumper.