Although I don't have it, the UAD stuff is what most of the professionals I know use - that and Waves if they don't have UAD. Not a large pool I know, so take it for what it is.
The basic UAD stuff (that comes w/ the card) is good. Most people get the classics (they are hardware classics for a reason) - the 1176, optical etc. Once you get the card you can demo the product for two weeks (I think) and see what you like before spending your cash.
For my own stuff, I use mainly the PC stuff - including the softube bundle and the opto comp. That pretty much covers eq and compression. I have the nomad stuff too that I'm fond of. Their blue tubes package is good for a change up in tone - the time based stuff is very good and useful and the pultec/fairchild models are good for a thicker tone. You could probably get most of the effect from the blue tubes channel strip. The newer Nomad stuff is supposed to be a step up in emulation - the neve etc.
But I am finding I'm using more and more clean stuff for mixing. If you get your "tone" when recording you can then use digitial toys to control volume issues and cut (and boost a little) eq frequencies. Saturation and distortion, I find, are best left to the analog realm. Not so spikey.
I think you'll find the UAD stuff like everything else - most users have no problems (many users here have no complaints) along w/ a few w/ glitches of varying intensity. Just be sure to be able to take it back if it doesn't work and gets you frustrated. Personally, I'm wary about spending more money on more digital comps/eqs since what I have already seems to work. I woudl like to be blown away and have to get something, but so far I'm unconvinced.
@