Izotope and EZ vs all the others

I have Ozone 6 Advanced so that's the only I'll be able to talk about. It's comes with Insight, which is an absolutely phenomenal metering suite. A lot of the Ozone modules themselves have some really useful metering tools as well. the EQ, Multi-Band Dynamics and Maximizer are the 3 that work the hardest when I master music, with the Exciter and Imager working just a little bit. I do find that the tools needed for mastering are covered very well by Ozone.
 
In all honesty, I will say that iZotope's plug-ins are arguably the best due to many reasons. The ability to use the History function as well as being able to save 4 different settings within the plug-ins and recall them instantly has been a huge boost to my workflow. I honestly wish all plug-ins implemented this in some form or another. These functions really allow you to tune your ear to many different settings quickly. It's audio ear-training on the job and that's incredibly helpful. Not to mention the plug-ins themselves are very flexible and powerful. I'm not sure you can go wrong with Ozone.

They also have an ebook for Ozone. I went through it a couple of times and it's a nice introduction on the application of their product in the mastering context.

I'll use the individual Ozone components on some of the busses in my projects, such as drums, guitars, synths etc... I do find it quite useful in that kind of 'stem mastering' context as well.

Take a look at the Voxengo line. The Soniformer and Elephant are my workhorse mastering plugins and they're quite affordable. The Soniformer is essentially a 31 multiband compressor that can help bring out certain aspects of a mix that were hard to achieve during actual mixing, and Elephant is a superb limiter that has a lot of features under the hood for dialing in settings for different genres of music and will offer greater gain reduction than the Waves L Series without sounding squashed.