In my own experience, American cars have been easiest to keep running. Fewer electronic glitches, fewer strange habits developed over time, less expensive to repair if something does go wrong. Granted, this is based on some older, more proven American designs (V8 engines in RWD chassis, both cars and trucks). There's not too much that can go wrong with them.
The imports that I've had have all developed their own quirks. The Honda kept going and going and I never had anything truly unexpected happen, but it did need more frequent maintenance attention than my father's American trucks. The old Porsches I've had have been every bit as reliable as the Accord was, but they too all had some quirks or required more constant attention to maintenance, little design "flaws" like the plastic sunroof gears in the Porsches that always strip, or in the Volvo, the door stops that have a disturbing habit of coming loose from the car allowing the door to swing open un-checked and the dash-mounted switches that break their tabs and start to vibrate out of the dashboard.
Overall, I think that imports had the edge in the 1980's for econoboxes and boring family cars. Cars like the Mustang and Camaro, because of their unsophistication, were worlds more reliable than, say, a Mitsubishi 3000 GT or an RX-7, and imported trucks were just plain a joke back then.
Now, I think that things are fairly even, with domestics still having an edge in the true truck market.
ZV