This one was mine, a 1998 Mercedes W208. The nice things about it were the cool Mono-Wiper, the engine (supercharged 2,3L M111) and the seats that were perfect for my height. It had a terrible ASR system but came with a LSD, so it was lots of fun in the winter.
The not-so-nice things about it were that the ignition randomly would not recognize the key, a missing catalytic converter, two fist sized rust holes in the front control arms, rust all over the underbody and the absolute worst 6-speed manual transmission I have ever used.
It also had multiple alignments but it didn't take long for the steering-wheel to be off-center again. You could see the tail end "crabbing" in the rear view mirror. There was something very wrong with it, which can probably be attributed to one of the 7 previous owners.
This isn't even counting all minor annoyances like the frameless windows not lowering themselves when you open the doors (that was only a thing after the 1999 model year), the wind noise, the awful interior materials, the broken seat latch in the rear, the trunk lock not working... I could go on for an hour like this.
So anyways, what is the worst car YOU have ever owned?
I don't beleive my worst car is anywhere near as bad as some terrible cars I've driven/borrowed/rented. Background: I've been driving since 2008 and have owned 7 vehicles with 4 wheels between my y wife and I. And it is a diverse range of slow, small, unequipped, unreliable, and unattractive. But almost everything was bought for the purposes they exceed at so I don't complain about informed decisions.
The only car I didn't really choose was my first car, a 98 Taurus inherited from grandparents. I could call it the most boring, or the most mediocre when weighing all metrics, but not the worst I've used for at least an hour. I had it for 10 years before rust made it too risky for a long commute. The cheap leather seats were durable enough, the power was enough (faster duratec), the interior was roomy enough for 4, the trunk as normal, and the wind noise was low (slippery dickens aero design). The appearance was a distinct product of its time, out of place by time I owned it - they went TOO round. Parts supply wasn't great on some key critical areas that did change over the years, such as coolant and transmission tubes. I could handle it now, but it's long gone.
The one that would resemble OP's situation remains my favorite, a Lincoln LS. Knowledge is what makes this one tolerable when it fails (by recognizing symptoms before catastrophic failure) and keep the memories net-positive. The handling is superb, as Ford/JLR sought to directly compete with BMW with this car and the Jaguar S-type (same chassis). Power was good for 2000 but didn't inflate to stay good by 2006, but the good noises offset the actual performance for me. But these things are notorious for misfires (which get misdiagnosed), overheating (which gets misdiagnosed), transmission issues (which get them replaced when they can be maintained better and fixed easier), need more frequent suspension rebuilds like a real BMW, and have a slew of unique parts because this is closer to a Jaguar than a Town Car. But every time I drive it, there's just something special about it.
A short version of what many consider terrible is a Geo Tracker and a 4cyl 90s Ranger. People call the Ranger way too slow. I'll tell you what's slow, a Geo Tracker. The Tracker works just fine, you just have to crank it out on on-ramps and hope no one jams your flow by merging at 20 under. But it's tiny size (smaller footprint than a Miata) is a treat to maneuver, the 4x4 is realer than a common modern suv, the convertible top masks the mediocrity with summer thrills, and the heater is one of the strongest I've ever owned for the "cold winters in a soft top". Meanwhile, the Ranger is a little quicker, happier to cruise on the highway, has more than enough power for a competent well-planning driver, and hauls bulky stuff the same as a bigger engine/pickup. I've had 800lbs of plywood and barely noticed a difference. I'll take the improved MPGs.
So what's the worst car I've driven for at least an hour in town, city, and highway? My dad's 2011 Hyundai Sonata. I don't know what went so wrong, but I just hated everything about it. I did my best to adapt and get comfortable, but it was just a terrible experience. It exceled at mediocrity. The interior materials were 20 shades of hard gray, the displays were uninformative, the doors closed with the sound of a door 30 years older, the buttons were unfriendly, the visibility was lacking, the front is hideous, the headlights are atrocious, it eats tail light bulbs, the arm rests are all wrong for me, the dash buttons and indicators all used deep blue LEDs for illumination which is atrocious to see at night (too much UV intrusion and blurring), and despite already being familiar with an 80hp Geo, this Sonar felt more underpowered with its vague automatic transmission and polite engine noise.