bitflipper
Most drum libraries fall into one of two categories: do-it-yourself or ready-to-wear. Superior Drummer is in the former, BFD the latter. Neither category is better at all things. Superior can give you exactly the sound you're after, but it'll make you work for it. BFD takes less effort, but unless you have the budget for lots of expansions you may sometimes find yourself settling for "close enough".
I would mostly agree with this,
except that you can definitely get to BFD's raw samples if that's what you want to work with. Just load a kit instead of a preset and you can adjust everything manually, with or without FX.
bitflipper
But if I was looking to add a Category 2 turnkey drum library, I'd seriously consider Steven Slate Drums. Although not as tweakable as Superior, it's one of the easiest libraries to quickly and effortlessly get good results with. Plus at $149 it's a steal - less than the price of one Superior Drummer expansion - and you get 100 kits.
These are quite good as well. Having SSD4 and BFD3 though, I can honestly say I reach for BFD more often.
Regards,
Dan