I've been a fan since they were sold by Mackie as the UAD-1. Currently I use a pair of UAD2/Solo cards, but I'm straining them. Which means I need to decide on the card vs Apollo... not as obvious a choice as one might wish!
There are a handful of UA plugins that simply have no rivals - at least to my ears...
The first time I heard the dBX 160 plugin I was transported back to the late 1970s, when those goofy things were ubiquitous in smaller studios. The plugin sounds exactly like I remember them - which is even better than sounding exactly like one.
The Ocean Way rooms can change the complexion of a track or a mix in magical ways - although figuring out how to use it well can be a bit challenging.
The Plate 140 is simply amazing... best plate emulation I've heard, and I used to use real plates.
The Studer and Ampex tape plug-ins are subtle, but I really like whatever it is they do. I probably prefer the Studer, but it's close.
The Cooper Time Cube is one of my secret weapons (along with the Plate 140 and the Maag EQ). So forget I said that.
I used to think that the 1176 emulation was awesome, then they revisited it, and since the new one can't be more awesome I'll just call the original great and the new one awesome.
There is not one plug-in I've tried that I did not like - although I do not own all of them - that would get quite expensive.
And there is a
chart that estimates the number of instances for any given plug-in on specific hardware. In my experience it is accurate, if not a tad conservative. That will give you a pretty good idea of what each device can do...
Be wary - you can end up spending quite a bit on plug-ins once you purchase the cards!