The all-new, third-generation 2017 Buick LaCrosse is both a near-luxury full-size sedan and a super-deluxe road mansion.

Let’s start with features the base, Preferred, Essence, and Premium trims have in common. The entire LaCrosse lineup rides on General Motors’ lightweight P2XX platform (shared with the Chevrolet Impala) and is powered by a 3.6-liter V-6 (shared with the Cadillac XT5 and GMC Acadia).

The prior generation’s eAssist mild hybrid was discontinued, but thanks to fuel-saving measures such as automatic stop/start and a feature that shuts down two cylinders under low demand, the combined fuel rating is up from 22 miles per gallon (mpg) to 25.

The base model also includes a new, eight-speed automatic transmission, Apple CarPlay, and Android Auto compatibility, sound-deadening measures and acoustic glass, 18-inch wheels, HID headlamps, and LED running lights and taillights.

The Preferred trim brings more exterior color options plus satellite radio, power adjustable steering wheel, polished alloy wheels, and a cargo net — for about $4,000. The Essence includes all of the above plus a panoramic sunroof, leather, heated front seats with driver memory, and an optional Driver Confidence package that features blind-spot monitoring and rear-cross traffic detection with audio alerts.

The real excitement begins at the top of the lineup, where the Premium edition comes with all of the above plus heated steering wheel, massage chairs, head-up display, and forward collision alert. Premium buyers can also add magnetic ride control suspension with 20-inch wheels ($1,625); adaptive cruise, auto braking, and automatic park assist ($1,690); and all-wheel drive ($2,200), which drops the combined mpg to 23.

The base LaCrosse competes with the Nissan Maxima and the Toyota Avalon; the completely decked-out Premium puts it firmly in Acura TLX and Lexus ES 350 territory. With its super-quiet ride and a sleek, sophisticated, and somewhat understated design, the LaCrosse holds a competitive edge over the entire group.

Better yet, Buick’s engineers were able to add 2.6 inches between the wheels, most of which can be found in the rear legroom, and bumped the outgoing model’s much derided trunk from 13.3 cubic feet to 15.0.

Fleet buyers who are in the market for a new executive sedan would be wise to include the new LaCrosse on their demo lists. It is in showrooms now, with starting MSRPs ranging from $32,065 to $44,190 for Premium with all-wheel drive.