My personal opinion....
...has Blazers on top of that list. Nothing compares to the one my parents owned. Everything about it was unreliable... Biggest POS ever. Same with the one my uncle had, my grandpa's S10, and other ones that were in the family. Engine and engine component problems, transmission problems, 4wd problems, electrical problems, problems with random things, and problems with being shoddy. The best thing that happened to ours was my mom flipping it and sending it to a junk yard where it deserves to be.
J-bodies... Don't get me started on these. My one uncle has owned enough of them (5 or 6) and he was always coming over and using our garage to repair them. Just about each time, it was a different one. Then there's our Sunfire. The first week we owned it, it had to be taken back to the dealership twice. The one my grandma had was equally as unreliable. Not to mention the Cavalier that used to be my aunt's, was then my other grandma's, then passed through our ownership, and eventually was donated to my uncle to add to his "collection" of them. A few friends of mine have had Sunfires that left them stranded as well. Come to think of it, no one I know has owned one that wasn't unreliable. Doesn't matter if it was a Pontiac or a Chevy, coupe or sedan, 2.2L or 2.4L, auto or manual... All craptastic.
A vehicle that never gets mentioned as being unreliable (atleast here, anyways) are Silverados. 4wd problems, brake problems, random things not working... All common problems with my dad's, my grandpa's, three that my one uncle has owned, and another uncle of mine's. All 2000s and newer.
On the other hand, I think Grand Ams have a worse reputation than they deserve. The two my parents were more reliable than anything else they've owned. Both with the not so great 2.4L Twin Cam at that. However, mine, with the Quad4 is pretty $h!ty, but mostly due to the engine. Other than that, it just had little things that went wrong due to abuse.