I had been assigned to develop a system on where we would get a XML from multiple sources (millions of xml) and put them in some database like and judging from the xml i would receive, there wont be any concrete structure even if they are from the same source. With this reason i think i cannot suggest RDMS and currently looking at NoSQL databases. We need a system that could do CRUD and is fast on Read.

I had been looking at MarkLogic and eXist, which are both XML based NoSQL databases, have anyone had experience with them? and any other suggestion? Thanks