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