TL Space feels pretty dormant to me as a product. The last time a product felt dormant to me, it was Lexiverb which was never ported over to OSX. Also, TL Space has very few true stereo [input] IRs, unless something's changed. Truthfully, I thought it had a lot of promise, but I got tired of waiting for it. And they were supposed to have their own app to custom sample your own spaces at some point: never materialized.
Altiverb has TONS of IRs and tons of stereo input IRs. It might sound better as well. I've kind of had that sense for a while now. And they have an app for custom sampling your own spaces.
TL Space: more and deeper controls to easily shape the reverb
Altiverb 6: no predelay
TL Space:I seem to remember that the PCI bus still 'chokes' when you change parameters while rolling. This has been going on a long time, which indicates to me that it is either incurable or the developers/owners don't want to spend the time/money to fix it.