The Buick Regal was a much more attractive design (for its time). The Regal shared its front clip with the Century with only minor changes (the turn signals were rectangular rather than circular and the grille mesh was fancier). In profile, the Regal coupe got the formal roofline and opera window that GM used to indicate Personal Luxury Car (just like the Chevy Monte Carlo, Pontiac Grand Prix, Olds Cutlass Supreme, and other, larger models). And the then-ubiquitous vinyl roof that was originally intended to give the appearance of a convertible (the term ‘hardtop’ was an oppositional reference compared with a convertible, or soft-top).
That deep sculptured line from the top of the fender and fading into the door meant that there was wasted space in the door. Just looking at the windows, you can see how much narrower the interior was. But I always thought this was one of the prettier designs of the era (the heavily sculpted Starski & Hutch Ford Gran Torino came out around the same time). The heavy pillars were due to proposed roll-over regulations that were never implemented – those standards killed convertible production anyway.
Along with the contemporaneous Ford Gran Torino/Mercury Montego, the GM A-body (and closely related G-body) models arrived on the market just in time for the 1973 OPEC embargo. They’d been designed to be heavier and more luxurious than the models they replaced. Similar designs will never be produced again because they were so inefficient and wasteful.