So far, it seems I like Nectar 2 for my vocal plugin, and I am eventually gonna need a mix/master suite. It looks like, for me, the competition is between Ozone and EZMix. Since I understand how they do things, I figure it's better to stick to what I know, than to go off on some vst treasure hunt(Waves as an example)? Plugins like DPro scare the heck out of me... TOO many controls... I like Nectar, pick a preset and tweak a bit.

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 have Ozone 5 and EZMix.
 
Ozone has more controls than EZMix. EZMix does not always get me where I want to go but when it does it's worth it.
 
I've never used Ozone on anything but as a final mastering tool (and I use the m, not M, in mastering).

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.

I don't know about EZMix but I downloaded trial copies of Ozone 5 and TRackS.  Ozone 5 won out for me.  Its what I use for mastering.  I also bought Ozone 6 but it is mostly unused.

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.

I actually hear some pretty good things about Voxengo's line. Their stuff looks quite interesting, but I am definitely not in the market for more plug-ins.

I invested in the TRacks plugins several years ago and haven't felt the need to try anything else.