ArcSyn

One of the best VA synths around. I use it on every track, it's my bread and butter synth, and I freaking love it.

Each and every feature is done right, especially sound generators and filters. The oscillators are clean and fat, they don't have that digital, bandlimited sound like old VSTs and some newer ones do - you really get a smooth, rich sound from every type of oscillator, and there are a lot - the basic ones are there, and they work really well, and then there are a lot of innovative ones. The best part of that, though, is that almost every oscillator type is modifiable via the Shape knob, so all sound generators have an easy, modulatable way of changing the sound from the start. Without touching the filters you already have plenty of sonic capabilities, and the most important thing, those capabilities are really at hand. In this synth, everything is one screen (no different Synth, Modulation and FX pages, although you can only view one LFO, one envelope, and half the mod matrix at the same time, all the oscs, filters and effects are visible).

The filters also sound amazing, and you have a lot of types - also some crazy ones, like the bitcrushers and comb filters. And since there are two, you can play with the routing to get more sonic variations. Also, even if this synthesizer's signal path is mono, you can easily set up a stereo sound by panning the filters and routing the different oscillators to each of them.

The modulation sources are also really cool. I have to admit I don't use the LFOs (sequencers) to their maximum potential, but they are really cool - and coupled with the modulation matrix, with the ability to combine modulation sources via math operations, there is no way you cannot get a living, organic sound from this.

Also it has audio in, so any sound that comes before this VSTi will get sent through the effects chain (if I remember correctly), so you can stack as many instances as you want in your effect chain. From version 4, the GUI is resizeable and there's also VST3 support, so yeah, really cool overall. And serial number activation.

Would totally recommend.