Why do so many people like Black and White? I personally think that all of the Pokemon in B/W are bland and unimaginative. Anyway, I would go with Soul Silver or Heart Gold.
Hmmm, Black and White Pokemon are unimaginative?
Voltorb, Electrode, Magnemite, Magneton, Grimer, Muk, Caterpie, Beedril, Weedle, Ledyba, Butterfree, Geodude, Ekans, Mareep, Sunkern, and many many more say hi.
Not that I dislike the earlier generation Pokemon such as the ones above, it's just that if you're going to argue that Black and White Pokemon are unimaginative, you're going to have reflect on the earlier Pokemon too.
Anyways, I suggest Black and White. It has the best soundtrack in the series, a more engrossing storyline than any other Pokemon game, some awesome new gameplay additions, and the Pokemon, while weird at first, grow on you extremely quickly. I was one of the people that hated the 5th gen Pokemon at first, but now they're completely awesome.