Best XML Based Database [closed]
You are right in saying that RDBMS would not serve the purpose even if it does support XML datatype these days. I have extensively worked in MarkLogic, and so far it is the best noSQL XMl DB you can have. I have also tried eXist, however it is not much scalable for production usage. MarkLogic gives agility in developement as well with integrated app servers and search engine. Currently it is serving terabytes of XML data in some huge publishing houses.
I don't have any practical experience with it, but I have read that IBM DB2 has special XML capabilities.
SQL Server has an xml field type, but imposes some restrictions when you have such fields in a table. An annoying one (for me), is that you cannot use such a table on a linked server.