I can't say they're the number one on the top of my list, but they're definitely the number two. They brought in a whole MESS of things that changed so DAMN much about how Pokemon is played now. B/W brought their own, full Pokedex, void of any Pokemon from previous generations, added the Hidden Ability to almost every Pokemon, updated the Power and Accuracy of many moves that were once too pitiful because of the lack of either/or, further changing the gameplay, and even went so far as to update many what were once useless abilities and actually made them viable choices, Sturdy more than likely being the most successful. They even brought in some of the most influential Pokemon in the metagames, with everyone knowing Ferrothorn being the most viable option for a defensive POkemon on any team, Conkeldurr being a great option for a super bulky attacker that can take more than one hit while dishing out hits like a truck, giving Politoed and Ninetales an actual chance in the OU tier thanks to their permanent weather abilities, making Venusaur an actual consideration in OU, and the list just goes on and on.
They may not be my favorite, but they were the ones that definitely had the most impact on the Metagame up to that point.
Not only the metagame, but the storyline was most certainly the greatest developed. As much as I don't like him, N really was one of the greatest Antagonists we've ever had. The ability to befriend any Pokemon including something that is thought to be unobtainable by humans, and he put it in a Pokeball.
Bianca started off as a small, weak little girl, and through every step she made she finally became the strong and confident (whether she realized it or not) person she dreamed she could be. She didn't participate in the big battle at the Pokemon league, but she sure was the first to rally up the Gym Leaders for their help with taking down the Sages.
These games have so many things that they offer to the franchise, but so many people brush them off too swiftly because of reasons like, "Omg it not genwun that best", or "i hate that there no previous mons" etc etc. Give it a shot, really. They're games that actually feel like their own game, rather than having tied so many elements from previous games into them, and I think it was a VERY good thing for the franchise as a whole.