Loaded question for me. Although each G is 90% identical they bring their own set of issues and benefits.
Best to Mod for Cruiser ( AC PW ect.. )
442 - 8.5 rear, nice comfy interior & trim, cheaper than a GN ( leaving more money for a 403 )
Best When New
Grand National
Best to Mod for Racing
Malibu ( lightest and has the SBC )
Best Seller
Monte, Bu, Cutlass ( as they have the highest production numbers )
Best overall
For me its either the LeMans 2 dr, buckets ,console, nicer dash, sharp syling vs the 78-79 GP
I like the hard body lines but would not buy one as they are harder to find body panels and trim pieces for