Speaking as an '80's cuber, the EARLY Rubik's brand cubes were not as bad as many posts on here seem to suggest. For a few years, they were actually screwed together, hence you could adjust them. None of the 'so tight they hardly turn' stuff that afflicted the later cheaper-to-make riveted mechanism. Plus, they lended themselves to modifications, as the plastic was fairly thick, so you could 'round off' the obvious square edges etc to give a bit of corner cutting.
The generic 'dollar store cube' gets my vote, they were bad in 1980, and they seem worse today. I spotted some yesterday in my local supermarket, stickered up with some cheap Christmas theme, nasty looking things. Probably made from 35 year old moulds.
( I like the earlier reference to blue-blue-green corners, made me laugh. And it reminded me that a girl in my class at school had a cheapo cube that had two green faces and a black unstickered face, it was a novelty to solve.)