hmm my issues with the EULA aside, i think SSD and S2.0 are quite different products.
SSD is all about pre-processed samples, that sound good out of the box, and if you don't want to dick around with settings for too long, SSD seems like a good option. slate knows what he's doing, and the fact he regularly visits these fourms, and gives support.. that's just unheard of. in that respect, slate slays the competition.
however, S2.0 was never meant to be a drop in plugin for instant good sounding drums. it's the raw, unprocessed samples of a kit (a few kits, really), it's up to you to make it sound good. i think a lot of people forget that!
there is a problem with the slate samples, and that's this; you can hear the slate samples a mile off. a lot of your own mixing uniqueness is lost because you're not really doing much with the drums. you can get such a hugely vast set of sounds with S2.0, with some work.
S2.0 was all about a natural, real drum kit. foundry is a more traditional (for toontrack) take on drums - it's a metal kit, and making it sound metal will be easier. but at the end of the day, the control is in your hands, how it sounds.
for me, S2.0 is better than SSD3.