These games does probably have my favorite soundtrack in the whole series. I might be biased since this is my favorite generation, but still. The music was really great all around.
From Black and White, my two favorite tracks are these:
The Credits. In my opinion, the best credits music in the whole series. I love everything about it, the melody, the instrumentation and how it suits the whole situation. You have just beaten a great game and for that comes some epic music. No other main series games tops this when it comes to credits music, and from the spin-offs, (the ones I have played) the only one that comes close is Colosseum.
Emotion. Another fantastic track. This does just what it is supposed to, it brings up emotions. It was played at the right moments in both game pairs and does everything right. I tend to like bittersweet or melancholic music when it is done right, and this is really done right. I was very happy when I heard this semi-randomly appear in X/Y.
Some others I like are these: Entralink, Undella Town, Gym Leader Battle, Marvelous Bridge, regular Trainer Battle, Battle Subway Battle theme, all legendary Battle themes, Rival Battle, N's Castle, Dreamyard, Opelucid City, Mistralton City, Nimbasa City, Route 10, Giant Chasm.
From Black 2 and White 2, my three top favorites are these:
Aspertia City. The best starting town in the series needs to have some great music. It did. I have several great memories from this and sometimes I went back to this wonderful city just so I could watch Unova from the lookout and listen to this wonderful music again.
Iris Battle theme. The best Champion needs to have the best battle music, and that was how it was. I like how this is rather varied without ever feeling messy, it contains several different pieces of melodies and instrumentations that flow together extremely well.
Black Tower. Another great piece of music with a genre I didn't expect to see in a Pokemon game. It is perfect for Black Tower, a somewhat mysterious tune for a somewhat mysterious and challenging place. I didn't get tired of it while on my quest to beat 1000 trainers here, and I almost want to go back and beat another 1000 trainers just so I can hear it again.
Some others I like (that weren't already in Black and White) are these: Floccesy Town, Virbank Complex, Colress Battle theme, PWT, Humilau City, Reversal Mountain, Route 23, Lentimas Town.