Heavy, Dry, and Loud MIDIPaks are all good, because they all have beats and songs. Plenty of variations. I also have Funk'd Up, Alternative Rock, and Percussion Beats. Funk'd up is really good! I got the Dry Beats and Songs to pair with the Vintage Dry kit, and the Percussion Beats to go with the Session Percussion kit.
As far as kits, I have both Fairfax 1 and 2, which are both good. I also added United Heavy and Black Velvet.
I think I lean towards United Heavy first if I need something loud, and Vintage Dry is versatile for just about anything, especially if you are looking for a natural sound. The Fairfax's are somewhere in between these other two, in my opinion. As far as Black Velvet, I tend to go to the other kits first, although I like a few sounds it has.
Session Percussion is always good to have, because it extends the range of your percussion setup. The grooves in the Percussion Beats MIDIPak are great too, and are designed for that kit.