I have thorough experience with all three of the plug-ins listed in the main thread post.
These programs are VST's and work as VST's. Sample Tank 2 XL has a standalone, as well as Hypersonic. Also, you can use Sonik Synth 2 sounds inside of Sample Tank 2. For instance, if you don't care for the interface, you can just install the sample library, and make a folder for it in your Sample Tank 2 directory, and use Sonik Synth fully and completely functional inside of Sample Tank.
Hypersonic 2 is solid. But it's a little dated, however it still sounds amazing. For lead synths, pads, bass, and for it's relatively extremely small size, it smashes on both Sonik Synth 2 and Sample Tank 2 XL.
Sonik Synth 2 has good atmospheric sounds and pads, and some good orchestral sounds, and guitar sounds. That is all. There are really hundreds, thousands of samples, that are junk.
Same with Sample Tank 2 XL. They are both very large, I think my Sample Tank 2 XL takes up almost 8 GB, and Sonik Synth 2 is a bit bigger.
I mainly use Sample Tank and Sonik Synth for Electric Piano sounds, Guitar sounds, and Orchestral, realistic sounds.
Hypersonic 2 requires a dongle, and the installation can be a bit of a headache if you run other Steinberg products.
But I've been using VST Plugins for quite some time now and for the size, I don't know how Steinberg created such an amazing plug-in under 2 GB. Probably because they invented VST technology? =) Very versatile and great sounds, almost every sound is use able.
Again, these products are very old.
Korg Legacy was very appealing, and still is to some, but Korg really lost it on the Wrapper. The plug-in doesn't wrap properly and most who use this product, run into major difficulties and end up re-installing and eventually getting rid of it, like I did.
It's all about ReFX Nexus now.
All you need to be focusing on is ReFX Nexus and it's many, many great expansions and updates. This plug-in is a beast, and I use it on everything, it's my main source for sounds, by far the greatest and is a true nex gen in VST/Soft Synth technology.
Full installation + all of the expansions, this monster takes up about 10 GB and well worth it. I can sit at my keys for hours, and not record anything, just playing around with all of the different high quality sounds this thing outputs!
Later.