A Town Car will (in the long run) be the cheapest to maintain, be the most reliable, and (depending on your driving) give you the best fuel economy. These can go 300,000+ miles before needing anything major, as long as maintenance is kept up. 1996 is a better year, as they weren't "cheapened" slightly to make way for the new 1998 models. If the intake is all plastic (peek behind the alternator, if it's aluminum, you're good to go. If it's black plastic, budget for a replacement. If you can do the work yourself, figure on $250-300. If a shop will be doing it, $700 is a good ballpark figure. These usually average mid-upper 20's on the highway, around 18-20 in town.
The Cadillacs of that era aren't as reliable, get low 20's on the highway, and do cost more to keep up. If you are going for a Caddy, I'd recommend the 1990-1992 Brougham (d'Elegance would be a bonus). Tried and true 350 (or 305) 700R4 transmission, very well built car that will last a long time. Typical early 90's GM issues, but nothing hard to sort out. If you go with a '94-'96 Brougham, you'll have the LT1, which is a very good engine, but the 4L60E, which can prove to be a problematic transmission. Just set aside some money for a good rebuild (or reman) when the time comes. Usually get to 130-140K before they grenade. Some last less, however. My truck is on 4L60E #3, at 134K. Trans. #2 lasted 17K, and it was a reman, by a very well known company.
Park Avenues are pretty decent, the 3.8L is a good engine, but I've known several people who have had engine or transmission failures in them around 100-140K. Parts are plentiful, but being FWD, access could be better.
