Waves for me

FabFilter and SoundToys!

1st uad
2nd slate and only for the virtual console channel since the uad console emulations are so heavy in dsp you can not use too much of them.

UAD

They all have pros and cons but all sound really good.
Haven't used UAD but I think they are the most expensive plugins and need external DSP (UAD card). But I only heard good things about those.
I do like Slate plugins. Pros: Really good sounding. Option to buy limitless plugins or monthly/yearly subscription. Cons: Single plugin licenses are quite expensive. iLok 2 required...
Makes sense for me, because I only use the tape plugin (and FG-X for quick demo mixes/master).
Waves has amazing and good sounding plugins.
Pros: Lots of plugins from basic to emulations to "special" plugins (like the bass/vocal rider, drum pitch, etc.); good sounding. No iLok required. Easy installation.
Cons: Lately focusing on unnecessary plugins. And I absolutely don't like their price system. You have to buy plugins first, there are sales every day, for updates you have to pay quite a lot for the expensive yearly update plan...
I purchased some plugin licenses because they were cheap at that time, never used those plugins, but still would feel weird not to update those. Anyways I've decided to stick with version 8 as long as possible. At the time version 8 plugins aren't working anymore I will not use Waves anymore. My most used Waves plugins are the NLS, the H-Delay, the API 550, the SSL bus comp, the RVox. I think that's it.
If you are planning on using plugins from one provider only I'd suggest having a look at the Ik Multimedia plugins and Plugin Alliance plugins as well. Fabfilter and Voxengo have some nice stuff too, but are more basic EQ and comp plugins. Actually they are the best for basic EQing etc. But if you're interested in emulations of different compressors etc. Plugin Alliance and IK may be good alternatives.
My list of versatile plugins providers:
1.) Plugin Alliance
2.) Ik Multimedia
3.) Slate Digital
4.) Stock Plugins
5.) Waves
not listed: UAD

The thing i like about UAD is like i have desktop i can have extra PCi card for processing the plugins. but I personally don't own any UAD they are really expensive. and more i am learning my views towards plugs is changing. Like I was chasing these Slate and UAD compressors but i don't know its only me who found fabfilter Pro-C2 compressor is amazing for all purposes. but slate Bundle option is great and has all their plugins for like $150 an year

It is worth mentioning (since people say uad is expensive), if you keep an eye on the web site , you can have the most expensive plug ins (350e) for around 100e or less sometimes. They recently had a bundle for 70% less the original price. This however goes for any plug in maker in the market....black friday is coming sooo prepare those wishlists

UAD is definitely being quite aggressive right now in the market, and they have some smaller, quite good interfaces that will offload a lot of processing power, BUT, thunderbolt 3 can be problematic if you're running a PC. I've been arguing with a TB3 expansion card for a few months now and it's getting frustrating..... (using a Apollo x6)