Toontrack is a good company! I have several of their products, and they seem to keep things up to date, and provide excellent support.
As a non drummer, I picked up EZDrummer rather than SD3, which meets my needs for now. It's good to know that there is an upgrade path! Plus Toontrack is always releasing new expansions.
I also have XLN AD2, and a number of ADPack expansions for it. It's still a functional product, but it now seems like ages since any new AD-Packs have been released. I will say XLN still provide updates and support, but don't seem very interested in leading the market...