Valerie, I personally love the Valhalla reverbs, I own Valhalla Room. It's what I use mostly for instrumental, ambient-ish music. I also own Izotope but it's too complex for me personally. I find Valhalla very clean and their interface is real simple, allowing to experiment with many settings quickly. I haven't heard artefacts in the trails either.
I haven't tried UAD or Lexicon, though... Maybe download trials and hear for yourself?
EDIT: I own and have used Waves TrueVerb for years too, and like it. But these are reverbs I could personally afford, so I haven't explored the upper echelons of professional ones.