It's gonna be a tie between every Ford we've ever owned.
Where to start.... transmissions? E4OD, M5OD, AOD, 5R55E, all sucked.
The 80-96 Ford trucks had problems with the passenger side dash board tearing loose from the firewall, the mirrors breaking loose inside the doors, the rear cab mounts collapsing, and the frames breaking over the rear axle.
The second gen Explorer is pretty much the reason why Ford doesn't own the SUV market anymore - all the people that ever owned one swore off the brand. Sunroofs leaked, rear hatches leaked, unit bearings and ball joints got replaced at every oil change, plus transmission problems, Firestone, etc. Edit: Oh, and the fucking motor! I completely forgot about the OHC 4.0 with the plastic timing chain tensioners.
The third gen Explorer was no better, and came with the famous howling rear diff and an extra set of halfshafts and wheel bearings to crap out on a regular basis. Also, they have the tailgate that self-destructs, and shitty 5R55E again. Oh, and broken blend doors in the dash.
Ford sells more trucks than anybody else for a couple of reasons - they sell between 30-40% of them into the fleet market (depending on the model). They totally dominate there. It's the reason every construction site is covered in Fords. Most of those trucks are fleet rentals provided through third-party management companies. That, and GM splits their sales numbers across a bunch of different brands and models. If not for those two facts, the F-150 best-selling record would have fallen a long time ago.
And the JD Power most-dependable truck on the road today? A fucking Chrysler. Who woulda guessed that?