keeping in mind that there are a LOT of factors in play here (personal taste, your ears, your monitoring environment, etc)...
I have an LXP-1, LXP-5, and PCM-90 in my rack. There is no question, in my room, to my ears, that the PCM sounds WAY better than the LXP-1. This applies to mixes as well as solo'd tracks. However, I only have one PCM-90, so unless I am printing I have to use it sparingly, and I have no problem substituting the LXP on certain tracks. In some cases I like the LXP better... but not often<G>!
As far as plug-in reverbs go, I'd have to agree with Mike, it's darned difficult to beat the Exponential Audio plug-ins. The Aether stuff comes close, and all of them come close to the hardware... in fact I don't think you can say that any one of the three sounds better. You might say one works better on a specific project, or even track, but they are all wonderful sounding reverbs. Another one that fits with this group is the UA 224... although it is a lot more difficult to use (can you really have too many parameters?) I also liked the Relab LX480.
FTR, I've had the good fortune to use the hardware 480 and 300, and they sound great! I might even be tempted to say better, but that would be based on memory, and of course some bias that comes naturally from being in the same room as these revered devices<G>!
I also tried the demo versions of the Lexicon PCM and LXP plug-ins. I thought the LXP was remarkably similar to my hardware, I could usually tell the difference, but I could not tell you which was which - or even which I liked better, they were slightly (slightly) different, especially for the LXP-5 patches. The PCM plugin did not fare quite as well, I almost always preferred the hardware version. I did not make a big effort to match parameters exactly because, well, because I already had the hardware and wasn't going to buy the plug-in, so I don't have any faith in that evaluation.
I think once you get into the realm of high end reverbs it becomes as much a matter of taste, or possibly ease of use (or even included presets?). If I were to purchase a reverb plug-in today it would be one or both of the Exponential Audio plugs. If they weren't available it would probably come down to Aether vs Relab, and I can't really tell which one would win... probably come down to price<G>!