Between those two I'm all over the '05 GTP. Reasons? More aftermarket support, in fact more support in general; the Grand Prix is a bigger car; the Grand Prix HAS A TRUNK (fold the roof and see how much room you have left) in the G6; and the Grand Prix will have a higher resale value down the road. A hardtop convertible is a "niche" car that won't have the same appeal to a broader audience that the Grand Prix will, IMO.