I would say everything with a good visual feed back (Vital, Serum, Omnisphere ).
When you can see what's happen in modulation, everything gets easier.
If your sound should be "spherical"/"atmo" a good visual saves you minutes and hours of work .

Of course the ear is "end customer" so this should be clear.

But If you want to go deep
My TOP 3
Msoundfactory
Voltage Modular (Cherry)
VCV 2

Honorable Mention Zebra 2

All are modular on my top list, because there are nearly no limits.

 

Surge Free VSTi: Free synth, basic sound design

J Riley Hill:
A basic overview of Surge the open source synth. I give a walkthrough of how to make a few simple sounds on this synth.
00:00 - Intro
00:51 - SuperSaw
03:13 - Wavetable
04:44 - Making a kick drum
08:00 - final thoughts

IT'S FREE!!! DOWNLOAD IT HERE: https://surge-synthesizer.github.io/

Vember Audio Surge is now open-source (Surge is available as a VSTi for Windows and costs €/$180.)

 

Last edited by a moderator: Mar 15, 2022

Mine favorites for sound design, from scratch (all 64-bit VSTi, under Windows 10):

DUNE 3 (Synapse Audio)
The Legend (Synapse Audio)
Discovery Pro (discoDSP)
Dreamsynth (Cherry Audio)
CA2600 (Cherry Audio)
Eight Voice (Cherry Audio)
RAPID (Parawave Audio)
Chromaphone 3 (Applied Acoustics Systems)
Vital (free edition) (Matt Tytel)

Also I like Voltage Modular (Cherry Audio) and Rack 2 (VCV).