I did a lab study in 2003?? Posted here somewhere.
Blackstone - is so-so in accuracy. Blackstone was slow for me.
Stinky/Cat - was quick. He was actually good direct service. Particle counts cool. Dunno about acuracy.
OA - is fairly accurate and the web results are quick - mailed reports are slow, though. Price is best for me as mentioned.
ANA - accuracy is lacking.