Gosh it is hard to say which car truly was the worst money pit/beater I drove...it seems that as the miles accumulate, so do your problems & repair expenditures.
Even though as a kid I liked the 72 Vega I bought, it rusted right through in the trunk bottom and had to weld in new metal all over the place from salt corrosion. That was the only car with 70k miles, that you constantly had to clean the plugs as it used a quart of oil for every two tanks of fuel lol. I give it a POS award !

I'd have to say my new worst car ever driven is a 1997 Mercury Mystique with the 2.5 Duratec V6. Loud and obnoxious sounding motor, PITA to do any service work to, and the cup holders didn't even work. Not to mention the ride sucks and the road noise is worse than riding in a 3/4 chevy with mud tires (not dissing chevy it'* just what I have to compare it to. I actually love that truck).

I've driven a few bad ones... '88 Ford Tempo, 99k, this thing was a turd, disgustingly slow with shot struts all around. Each bump would have you bouncing for a minimum of 4 seconds. Gas engine that idled like a diesel. Sloppy shifts. But I rather liked the plush maroon seats and the dash was tolerable.

'89 Ford Probe GT. Gorgeous car, and I drove it in '98, and it was always a car I had secretly loved as a GM nut. Then I got behind the wheel... Toasted throwout bearing, radiator fan on a toggle switch, turbo failing... Not to mention the idiotic turn signal lever and crap, but I didn't mind the gauges.

'94 Toyota Tercel. Bright blue, with black vinyl seats... NO AC... In the summer... Only the front driver speaker worked, and it was blown... Wait, a 4-speed manual? Running on 3 cylinders... You literally had to bounce it off the rev limiter and then quick-shift to the next gear to keep it from falling on its face... It was a shop car for a crummy buy-here, cry-here dealer. We literally abandoned this car, with no plates, key in the ignition, in the parking lot of a high-end resort. A week later, we brought it back. It was such a POS that nobody even wanted it!

...And every GM vehicle with a Rochester carb. Period. Eff that.

It was a mid 90s Toyota 4 Runner, that had been beat to hell, I first had to jump it, and then driving it back to the auction house I was working for syrupy brown liquid erupted from under the hood, like blood spray in a bad kung fu sword fight, covering the windshield...I swear I heard Brak, "Where'* the blood spray?!" Second place was a GMC Savana. We almost bought one, till we luckily drove through a bad tropical storm, that van was wallowing worse than a keel-less boat. Really dangerous to drive. The suspension was so horrible it made my sister sea sick.