I prefered BW, although B2W2 had features that I really liked.
I really enjoyed that Black and White only had new mons, as it was farther away and I was really disapointed when I found out you could catch old mons in the sequels prior to beating the game. (I know i'm in the far majority here, but meh)
BW also had a better story, the B2W2 story was simply obvious big bad is bad, while in the originals, for the majority of the game you are faced with a moral dilemma. Is it wrong to force pokemon to work for you?
However, I did like that they added to the region overall, as it felt very small in BW, im glad that they were actual sequels instead of just the usual third game nonsense, even if I wasn't the biggest fan of the way they continued the story.
There were also the Hidden Grotos, The Habitat mode pokedex, and a few other features that made B2W2 for me.