When most folks think of prestige automobiles in the grand American tradition, they're thinking of a short list--Lincoln and Cadillac. But that list is a bit too short. After driving the latest Park Avenue Ultra, we think this biggest of Buicks is a strong rival for the Lincoln Town Car or Lincoln Continental. Completely redesigned last year, the Park Avenue--and its supercharged variant, the Ultra--has all the attributes that traditionalists have treasured over the years: subdued luxury, living room comfort, high quality, excellent road manners, and all-weather reliability. For folks moving up from mid-size to full--folks who don't feel a need to fortify their status with something from BMW, Lexus or Mercedes--a Park Avenue is worth a serious look. It's a pleasant step up into quiet, roomy luxury, bolstered by high quality and a much more authoritative set of dynamic capabilities. Because it was redesigned for '97, changes to the '98 Park Avenues are minimal. The side mirrors now include a fold-back feature, the right-side mirror tilts down during back-up maneuvers, and GM's excellent OnStar satellite communications system is available as an option. We prefer the livelier performance of the Park Avenue Ultra with the Gran Touring suspension package, and that was our test subject. However, with a base price of $31,340, including destination charges, the standard Park Avenue stacks up as an exceptional buy among large cars. It's well equipped in its own right, and if the Ultra's extra performance isn't important to you, the standard Park Avenue may be the way to go.