I'm generally not a huge fan of softsynths, probably because I think most of them come across as "strident", "brittle" or "glassy-sounding" in terms of their overall timbre. Fortunately there are a few exceptions, one of which is Native Instrument's Reaktor which, depending on the instrument loaded, can sound absolutely lovely!
NI recently released a new Reaktor instrument, or "ensemble" in NI-speak, called Spark. This little gem passed completely under my radar as they marketed it more as a "sound library" for their Kore product line rather than on its own merits. Let me just say at the outset that, if you own Reaktor 5, Spark is well worth the fifty nine dollars they charge for a download.
Born from the Mind of NI's founder Stephan Schmitt, Spark is a fantastic-sounding synthesizer with a ton of character! The signal chain is eclectic even for a softsynth as the oscillator section is relatively simple in structure with much of the timbre shaping being done downstream. The tools available include a gutsy filter, a frequency shifter, an eight pole filter and multiple modulation and feedback paths.
The sounds I've gotten with this beast are both subtle and evocative. It's easy to create anything from an evolving/etheric pad to a gritty broken-guitar lead or a rubbery bass. Many of the timbres have an unusual organic feel, very unlike many other Reaktor Ensembles or stand-alone softsynths I've played.
Spark is well worth a look if you have Reaktor, maybe less so if you only have Kore or the free Kore Player as there's no direct access to the GUI, but it still may be attractive for some due to its great overall sound character.
Spark is a very welcome and unique tool amongst a vast ocean of mediocre, mostly-VA softsynths.