I love audio engineering, digital signal processing and pretty much anything dealing with creating, capturing or modifying sound. This year, I switch over from Pro Tools to Logic Pro and in the process I got the chance to revisit plug-ins. After a few months of research (and recommendations from friends), here are a few thoughts on a few popular brands.
Positive Grid's Bias is great for guitarists new and seasoned. For new guitarists, they offer a service called Tone Cloud which allows you to download guitar stacks that emulate famous musicians such as Dimebag Darrel, Jimi Hendrix, Kirk Hammet, etc. For experienced musicians, each plug-in pretty much offers you the ability to tweak every aspect. It's pretty nuanced and impressive.
Good Hertz makes great sounding audio with an even better UIX. These guys really understand why skeuomorphic designs are a thing of the past.
Slate Digital offers you a bunch of plugins for only $15/mo. This is incredible because there's nothing more frustrating than managing dongles (iLok) and 3rd party installers (Pace, Waves Central).
Waves really pioneered the audio plug-in space and therefore they deserve credit on a few things. First, they're doing incredible work partnering their plug-ins with name brand engineers (Jack Puig, Chris Lord Alge) and producers (Butch Vig). They've also partnered with established studios (Abbey Road) and console brands (SSL Series). So a lot of what you'll be paying for is name brand recognition. That's not terrible but it's just important to understand where your money will go.