The only thing that I not like in Pristine Space - it`s Zero Latency mechanism, Zero Latency setting can work bad if interface buffer length is not power of 2, plugin buffer shorter than host buffer is not very efficient method because you will need adjust buffer closer to host buffer length for maximum efficiency.
KeFIR is also good in terms of precision, but eats CPU with moderate impulse length.
My old test table:
My terms about good convolver:
1) Precision comparable to mathematical software
2) Zero latency
3) "Reverberation-grade" i.e. low consumption with impulses of several second length
4) Multirate i.e. quality automatic impulse resampling to different project sample rate.
I`m solve 1) and 2) in my own convolver (PFF Convolver) but currently have troubles with CPU consumption with large impulses (around 1 second is comparable to SIR2 or Pristine Space) and working on quality resampling