I'm getting really good solve rates using CaptchaTronix OCR for double blob recaptcha. Was really surprised at the performance of OCRs and the speed after trying for the first time today I had to put it in my signature lol.
Before I was using Anti-Gate/Anti-Captcha and I saw they were doing some double blob solves within 7 seconds so I think all services use an OCR to make extra money. Human solves seem to take as long as 40-70 seconds on there so when compared with OCR, even if average accuracy is between 45-65%, you will save a lot of money and solve faster than human solvers.
They're currently working on adding a total over 650 different captcha types. Highly recommend checking their service.