How do you count this? What's the rationale for saying that Excellerate was the next-best incubator after YC and 500s?

Forbes put together an analysis in 2012 (the last year Excelerate was still Excelerate) based on companies' exit price or price of most recent round. Excelerate came in No. 6.

http://www.forbes.com/sites/tomiogeron/2012/04/30/top-tech-i...

I don't know the methodology of the research but here is the coverage -

http://tech.co/top-startup-accelerators-ranked-2012-08