For me, in experience, the hardest to do was my grandparents twin 1997 Escorts (we had a 1997 sedan and a 1997 wagon for a few years before we traded the wagon in) Ford cylnder air filter with the air filter hoop on it, pain in the bottom to get on and off if you have big hands.
Easiest, tie between my 1992/2003 sable and our 2002 focus. The focus required screws but was a flat head screw, and it lifted verticaly, and the sables clips for the air filter which lifts out easily.
Easiest: 2006 Focus i owned, it had no user replacable air filter, it had a lifetime air filter in the fender that never needed replacement as long as the car was running, ford fitted a restriction gauge to the intake to allow you the ability to check if it was going bad (and if it did, it was expensive, but i have never seen one go bad)
For oil filters, easiest was that 2006 focus, right on the underside of the engine itself, behind the splash shield, it was moutned verticaly as well.
Hardest: 1992 mercury sable 3.8L, due to the fact that it was right next to the exhaust exit for the engine bay, and was mounted diagonaly to the engine, allowing for oil spill on the exhaust.
2003 sable is easy to get to, but is behind the exhaust, so it falls between those two.
Oil Filter:
Air Filter: