I have both and have run them side by side on gsa and Captcha Breaker beasts CS hands down. The success rate when using GSA is about 75% for CB and about 50% for CS. I have been using CS for about a year now and think it is a good product with great support but you can't deny the results with CB. I had the same question a week ago and decided to just buy CB for my second vps. Since I already had CS running on my main VPS I thought I would use the free trial and see. Within an hour I made the purchase for the full version of CB. I have left it running since Sunday and it has already solved 8K out of 11K attempts. This is with GSA and I have not tried with other apps but I am very happy with the results.
BE VERY CAREFUL WITH WHAT YOU THINK IS 75%.
Al this stat is:
The # of captchas sent to CB that have been attempted to be solved. It has NOTHING TO DO WITH SUCCESS RATE! You are being completely misled.
This stat is not even available in CS as it is pretty much USELESS. But alas, you will see it in the next verions of CS

Also, FWIW, I run them side by side pretty much 24/7. Im getting the same link yield in the same time with both products.
Also the # of supported Captcha types is bogus. It will count the same captcha as different types if it is a different color or size. CS does not currently count captcha types like this. To me a single piece of code which produces a captcha is a single type. But whatever, ill start counting like this too... for marketing purposes.
Also regarding updates, support, etc:
I work on CS everyday. Most days ... 8 + hours. 60-80 hrs per week. If this is considered lazy, then I am GUILTY AS CHARGED
There is a new version almost on a monthly basis.
Coming from a very large development house has, it ingrained in me to do regression testing on every feature of CS for at least 24 hours. I hope you guys appreciate that Im not pushing out much with bugs and then subsequently 'fixes'. To me, this is very counterproductive, costing a large user base LOTS of time and money. with bugs/fixes. Just a difference in philosophy ...
Also, our service speaks for itself. Just check the sales thread

We answer support 7 days a week and I have had the pleasure of speaking directly vis skype with many of my customers.
Yes, thats right REAL TIME skype support

And you get to speak with the developer himself.