I'm in the camp that believes all EQs are the same. Well, that's a little too broad - differences do exist, but they are in the number of features and the user interface, just not in the filters themselves (assuming they're properly implemented). Pro-Q touts great filters (with a name like Fab
Filter they'd better be) but in truth there are plenty of high-end EQs out there with filters that are just as good. (Ignore anything you read about "cramping" near Nyquist - it doesn't apply to quality equalizers.)
Pro-Q will not magically make mixes sound better, any more than any other equalizer will. If you know what you're doing, SONAR's bundled EQs are more than adequate.
That said, I have to admit that Pro-Q is
almost the only equalizer I use. Here's why:
1. Efficiency. Having 30 or 40 instances in a project is no problem, even on my low-spec machine. Part of this efficiency is from using your video adapter's GPU for graphical acceleration. With my other plugins that feature spectral animation, CPU usage is noticeably higher when the visuals are turned on. With Pro-Q there is no obvious difference in CPU whether the spectrum is enabled or not.
2. Ease-of-use. As with all FabFilter products, the UI is ergonomic, fast and friendly. For example, I use the band-solo feature a lot, and although that feature isn't unique to Pro-Q it's implemented very well. Using the mouse's scroll wheel to vary the bandwidth while soloing makes it easy to zero in on offensive resonances. Scroll wheel works for all knobs, too. There are other basic features that
should be standard on all EQs but aren't, such as being able to type in precise values for any parameter, hiding controls that aren't needed, un-do and re-do, A/B comparison, and ctl-click reset. The UI size is just right, IMO: not too tiny for my old eyes, not so big that I can't fit several instances onscreen. The spectral display can be either pre- or post-EQ, and offers four vertical scalings. Metering is pretty good, too.
3. Mid/Side processing. Another feature you don't see on every EQ, and again very well-implemented. You can have any combination of filters that apply only to the Mid component, only to the Side, or both, and all are displayed together in a visually clear manner. Ozone's EQ, by comparison, also has M/S support but you can only see M
or S at one time, so you can't easily see where they overlap. Before I had an M/S-aware EQ I didn't know what I was missing. Now I use it quite a lot, especially for mastering. You can also use Pro-Q as a broad M/S balance control for narrowing or widening the stereo image.
4. The Filters. Although some complain that Pro-Q lacks some filter options (e.g. no Baxandall) I don't miss them. Some of my other EQs such as Meldaproduction's MDynamicEQ and Voxengo's GlissEQ offer exotic filter types (e.g. band-shelf, harmonic series) but I rarely use them. Pro-Q lets you have up to 24 filters (!) with continuously-variable slopes up to 48dB/oct, so it's possible to create just about any shape you want. You can choose between linear- or minimum-phase, zero-latency or variable latency. Filters can be applied to just the left or right channels if needed.
Everything can be automated.
What's missing from Pro-Q? Certainly nothing I need. Some whiners complain about the lack of upsampling, but they apparently don't understand what oversampling is for or they'd realize Pro-Q doesn't need it. A resizable UI would be nice, but as I said the existing size is just right for me. I've read complaints that Pro-Q is too clinical and adds no color - as if that was a weakness! If you want harmonic distortion, use a distortion plugin. GlissEQ remains unique in its ability to stack multiple spectra; Pro-Q doesn't have this, but AFAIK nobody else does, either. It would be a cool feature. Pro-Q is also not dynamic, but I think making a separate plugin was a smarter move than sticking it into Pro-Q.
That's about all I can say about Pro-Q at this time; the above is all from memory as I have no working DAW at the moment.