That Buick is beautiful. There is one of those here in town, owned by an older couple that looks just like that. I love the look of this land yacht.
The only thing I see that needs attention on the blue one is the bumper fillers, and they will be a bear to find! I would clean the rust starting under that mating surface, then spray with rubber stone guard to keep it from reforming. Other than that, both the Buick and the Olds are beautiful. That is what a top of the line interior SHOULD have looked like all the way through. The earlier ones just did not measure up to my eye.
I'll take the blue one. Appears the bumper fillers are available... http://www.autobodyfillersusa.com/servlet/Detail?no=2
I was going to point out that the bumper fillers are available, but there is already a link. They are both quite nice! I'd like a GM and a Lincoln big car to add to my '78 New Yorker Brougham Salon (even the name is long!) for a cool big-car garage. I've been there before, when I owned a '62 Lincoln ragtop, '66 Cadillac CdV, and a '73 Imperial Lebaron 4-door hardtop, all at the same time. The '62 was show-ready, the Cad was in excellent shape, and the Imperial was in similar condition to the Buick shown.
$233! They sure are proud of these plastic bits! I think I'd take the Olds over the Buick on this deal.
I prefer the Buick. The Buick 455 is, to me, the best of all G.M. engines. Surprisingly, on the highway, it gets better mileage than the 350, and THAT is from a G.M. cross country mileage test using cars that were identical other than engine.
If I recall correctly, the Buick 455 also weighs about 100 pounds less than a Chevy small block. The front-mounted distributor is also a plus for fitment and servicing ad there's enough torque on tap to unhinge an oak tree.
Carnut reports that the Buick 455 weights are higher. Buick 455 640# Olds 455 605# Chevy 350 575# http://www.carnut.com/specs/engdim.html
Both are beautiful cars, but I'd go with the Buick, also. I've always liked those Buick chrome-plated wheels and fender venti-ports, plus it has the fiber optics lamp monitors, which I don't think were available in those years on the Olds 98. Still, it would be great to have either one in the driveway!