I own both reaktor and absynth, I use both for sound design and electronic instruments patches since years. Reaktor at this price is a solid deal, even if you don't think about building your own instruments. Absynth is pretty good for ambiance, evolving atmosphere, especially if you add the waveforms pack from Galbanum (
Galbanum | sonic science aural allusion | Architecture ABS ).
Since version 5 Absynth is running really better with PT, reaktor still a bit shaky but it's not that bad once you've figured out the file management system.