Decisions, decisions...
Going by appearance, GS all the way! Looks cool! The GN looks like a box on top of another box.
Going by acceleration and general performance, GN. Lighter, better handling, just about as powerful, it's supposed to pull away from the GS, if not exactly disappear from in the distance...
Maintenance? Hmm... they are both old cars now. Parts are probably still being made for both, although not necessarily by GM. But the GN uses an engine management computer and systems inaccessible to and unusable by a shade-tree mechanic, and if the systems are unavailable, the car won't run. Advantage, GS.
Which would I rather have? Well, being superficial, I'd go for the GS. However, what I'd really want is a Firebird Turbo Indy Pace Car with the GN drivetrain; the ONLY F-bodies with the GN drivetrain! Now, if Buick had an F-body, then I'd choose that...
P.S.: The 1970 GSX was available as a convertible, wasn't it? If so, F*** THE GNX! GSX Convertible all the way! Hell, even a Skylark V-6 Convertible over the GNX or a GSX coupe!
P.P.S.: I read elsewhere in this forum that the GSX was not available as a convertible. RATS!
Anyway, IMO, the most beautiful Buicks ever, and one of the most beautiful cars I've ever seen (and I have seen one in the metal) were the '71 - '73 boattail Rivieras.