I find Altiverb to be the best convolution reverb out there. Waves IR-L has an advantage only in the Virtual Acoustics digital convolutions that comes with the additional dvd. (Could you install those into Altiverb? Not sure..). I have both but would definitely go with only Altiverb if buying only one. They both win over Space Designer, although SD is also decent.
Redline Reverb by 112db is fantastic! I really recommend having not only a convolution verb, but an algorithm one as well. I find algorithm verbs works better on complicated/dynamic sources that changes quickly over time.
I find myself often using one of each within a project.
Redline is better than Waves Trueverb
, R-Verb, Breverb, all Logic ones, and some other ones I tried. Just my opinion.
Although Breverb IS nice if you're going for that 80s, super-lush sound, just a bit too unnatural for my taste. Might be really good for a song with only electronic sounds though..