xduce ocamlduce
Very simple API, adapted for one-off project and not too broken xml (like html for instance).
An implementation of XQuery.
(2008-10-29) The only Ocaml XML parser that can handle the complexity of the MathML2 DTD.
Handles unicode.
Still maintained (2008-11).
Simpler than pxp and more complete/correct than xml-light. One single module. BSD.
Xml-Light or Xmlm are probably easier to use than Yaxpo. Yaxpo provides the weird reentrancy stuff enabled by the astounding fallacy of an XML parser written entirely in CPS.
Tree automat e.g. can provide a good middle ground between efficiency and simplicity. The problem you might run into is that XML is a tricky format to deal with and some of these tools will choke up on complex files (namespaces,switching character encoding, weird entities in the DTD etc..).