This may sound strange, but it depends on the trim level.
If you go all out, I recommend the Pontiac Grand Prix GTP with the Series III supercharged engine.
If not, I'd get a Malibu.
Why? Well, I'd prefer the newer Epsilon platform of the Malibu and fully redesigned engine in the LS Malibu to the older 3800 engine and refined but still a W-body platform of the base Grand Prix.
So if your choice is Base Grand Prix vs. LS Malibu with the 3.5L V6, I'd choose Malibu.
If base vs. base, I'd choose the Grand Prix. The base Malibu's 4 cyl. really isn't that thrilling in a car the size of the Malibu, and is far outclassed in torque and horsepower grunt by the 3800 V6 - which isn't a bad engine (just old), and gets good fuel economy.
If LS vs. GTP - the Grand Prix. The GTP (esp. with Comp G package) is too cool, and has refinements and performance improvements galore, including improvements to the supercharged 3800 engine that truly earn it "Series III" status with a horsepower bump (unlike the base engine that only has emissions improvements).
Is that confusing enough?
