Bear in mind in Black/White (but not Black/White 2), you encounter ONLY new pokemon until the postgame. An upside of that is that the new pokemon are better balanced so there's less in the way of pokemon that are much worse than your other choices.
Well, Black/White 2 would probably suit you pretty well, except I can't imagine it being anywhere near as enjoyable without playing either B or W first. That said, I'd go Platinum. It's got lots of older mons but with a new story. It suffers from some momentum issues story-wise, but I think it's a whole lot of fun and a great improvement over D&P. Also has really great music and probably my favorite "rival" ever.
hg/ss then get b/w1 (I hated b/w2 because I didnt like the pacing) --- i7 3820@ 3.60GHz| 16GB Corsair Vengeance 1600MHz DDR3| Gigabyte GTX670 2GB OC| Intel 520 Series 120GB SSD| Antec EarthWatts 750W Green