Impossible to say.
That's like saying "Who is healthier, a 40 year old, or a 45 year old?"
Without checking out the physical condition of both, down to every detail, there is no way to compare.
The 45 year old might be running marathons. The 40 year old might be near death.
Same with car miles. 135000 sounds like a lot, but how were the 100,000 miles of the Cougar gained? Was it maintained the whole time? Driven gently? Etc?
Nevermind that 135k miles on a 1991 car works out to 7500 miles a year. National average is around 12,000, so that's actually a LOW mileage car.
And without knowing the complete history of both cars, driving patterns of the owners, maintenance records, etc....there is absolutely no way to accurately compare the two.
As far as more reliable.....that's on YOU. The car doesn't maintain itself, repair itself, etc. So, either one will be reliable, as long as you take proper care of it.