Other previous posts were about Oakland and Pontiac, Oldsmobile and Viking, and Cadillac and LaSalle.
Some background I provided earlier: "A major factor in the rise of General Motors during the 1920s was Alfred P. Sloan's establishment of a price-prestige hierarchy for GM's various brands. Over the 50 years from 1941 to 1991, when the Saturn brand appeared, the hierarchy from low to high was Chevrolet, Pontiac, Oldsmobile, Buick and Cadillac. But during the late 1920s so-called 'companion' brands were introduced to fill what seemed to be price gaps in GM's line. In 1930 the hierarchy was approximately (there was price overlapping in a number of cases): Chevrolet, Pontiac, Marquette, Oldsmobile, Oakland, Viking, Buick, LaSalle, and Cadillac."
So Marquette was roughly atop the entry-level range, whereas Buick was positioned a little below the luxury line. Buick's lowest line, Series 40, had wheelbases of 118 inches (2997 mm), while Marquette wheelbases were 114 inches (2896 mm).
Buick 40s and Marquette's are compared in the images below. Unless noted, photos below are of for-sale cars.
1930 Marquette Model 36S Sport Coupe
Marquettes had an interesting (for the time) slightly V'd grille design.
1930 Buick Series 46 Coupe - Mecum Auctions photo
The Marquette coupe and this Buick coupe might well have shared the same basic body -- note doors, windshields, and even fenders.
1930 Marquette Model 36S Sport Coupe
But the passenger greenhouse and hood are shorter than the Buick's seen below.
1930 Buick Series 46 Coupe - Mecum
The trunk / rumble seat zones do seem the same.
1930 Marquette Model 30 Sedan
Comparing sedans ...
1930 Buick Series 40 Sedan
Door hinging seems the same. But the Buick's passenger compartment after end extends farther.
1930 Marquette Model 35 Phaeton - BaT Auctions photo
As noted, the grille is distinctive due to its V-profile. The chevroned grille bars are another distinctive touch.
1930 Buick Series 40 Sedan
Grille framing is standard Buick, similar to Packard.