Zahid, this kind of response is not helping anybody.
You sound like a school teacher that has marked the answer wrong because he knows what the real answer is.... (Something like 'thank you, but I'm looking for a bit more' will actually encourage fellow forum users to assist.)
As Gaurav pointed out - each vendor will only highlight their own good points.
There are independent analysts, for example Gartner. If you go to their website, you can download their reports at a fee.
Else, you have to trust vendors that have purchased these reports and published it.
See if this helps: http://www.symantec.com/content/en/us/about/media/industryanalysts/Gartner_Clustering_Software_Market_Dec09.pdf
