I've mostly selected midi paks for styles that require a lot of work because they're complicated, or styles I'm not so good at, that is all the funk stuff (funk beats 1 & 2 and Funk'd up) and jazz patterns, I do also have vintage dry and reggae midi paks but I rarely use any ready made midis unless it's a lot of work. The kitpiece selection is pretty limited and I have most of the ethnic stuff in other libraries, so I've mostly selected snares and kicks.
I have also Indie, Funk, Jazz Brushes and Studio Rock adpaks but Vintage Dry, United Pop and Modern Soul and R&B get most use, however none of the other ones are bad, I just use them less. The Studio Rock is one of the oldest kits though and I bought it only because I got it really cheap. leo007 has one for $10 on the for sale-section.
If you buy a bundle, you don't have to select everything in one go, so you can just pick one kit and play with it and then select maybe a kitpiece or midi pak next month, the site keeps track how many activations of each you have left for each.