Hi Manoj,
It depends on the feature sets you need. My opinion is that Liferay is the most polished one.
I also tried
JBoss Portal and Liferay. Now it seems that eXo platform joined JBoss community and it will be merged into JBoss Portal. This fact at the same time it means that JBoss Portal weakness and if you wait some time maybe JBoss Platform will be more advanced.
Anyway, at this time Liferay has the most advanced features and it has a very flexible access control mechanism.