The latest one always seems to be my favorite. 

The one that is really growing on me the most would be The Evil Drums by Platinum Samples.  I like Rail’s presets more than the namesake’s presets though.  Probably because my vision for drums is more in line with his.

I was trying to consider which collection would be the first to be deleted if drive space was an issue.  (I have them all.)  After a minute or two of consideration, I decided that I’d just get a 2 terabyte drive and keep all of them.