Being Oldsmobile is my favorite GM division, and I know my division.
I would go with the Ninety Eight on one simple fact:
The 3800 under the hood my experiences with the car.
The Intrigue is a divisional car and rides and handles well has a few short comings. What is under the hood is one of them. I think long term with vehicles. I have ridden in an Intrigue and other Oldsmobiles. I do not trust Shortstar as it is derivative of Northstar and can be expensive to repair or fix. That 3800 in that Ninety Eight is common and parts are around in abundance. All the bugs had not been worked out of Intrigue in 1999 either. They had used the 3800 and switched over to Shortstar. There also were too many little electrical issues on this car too. While it looks great and is a fully loaded GLS, I would pass on it. In in terms of W Bodies of that era, The Oldsmobile looked the best, and offered a lot. The Regal and Century just were not up to snuff in appearance or performance. The Grand Prix was the best all around performer during that time. Chevrolet was the most affordable package( Monte Carlo and Lumina).
I would go with the Ninety Eight because :
1. It shares parts with Eighty Eight, LSS, and the 1995-1999 Aurora. This will prove handy.
2. It is quite the car especially on gas. I know.
3. Comfort, convenient, secure.
4. The design and quality was all ready set in and improved during this time.
5. It also has mechanical parts in common with Buick Park Avenue
Find out if that Ninety Eight is a Series I or Series II
Series I: Has no digital gauges or memory seats( control is on drivers door.It will say 1 and 2 and set)
Series II: Has digital gauges, information center, memory seats and more.
Lets put it this way.. The only difference between my car and a Cadillac is I do not have a V8. That is it. In fact The Ninety Eight had more features than a Deville. I know. The Deville did not get passenger side climate control and steering wheel controls until 1997.