is there any website or papers that gives the ranking of various exe protectors ?

Ranking in what context? Most prevalent? Most difficult to remove? Etc.

sorry for not being clear, the packer that is most difficult to remove and how regularly updates are done on them. Themida i thought was very good, and saw similar comments on the net. Just wanted to get the views from here, ranking exe packers from top to bottom in the decreasing order of difficulty (most difficult will be at top). This study won;t be complete in any sense without taking inputs from this forum .

Pretty much all most used packers can be removed automatically nowadays. (Armadillo, Themida, Asprotect, Execryptor, VMprotect.) There's a few exotic ones that are not that much automated, but those aren't that hard either. Most have also been keygenned or can be cracked without licenses. Some of the above when doing manually can be very hard. But well manually is not longer necessary.

VM interpretation still is not that common but dumping VM's is easy and most antidumps have been documented. (VMprotect has none documented, but those are only CPUID and heap antidump not very fancy.)

IMO, Themida and VMprotect are good Exe Protectors. I'm not sure about the others though, never did try ;D