I don't know StAX, but I can say something to DOM and SAX:
Dom holds the XML-Data in memory as a Object-Model. The advantage is, that you can access and change the data in a convenient and fast way in Memory. The disadvantage is, that this has a high memory consumption.
SAX uses some kind of an event-pattern to read the data and doesn't keep any data in memory. The advantage is that this is relatively fast and doesn't need much memoryspace. The disadvantage is, that you have to create your own data-model if you want to change the data in a convenient way.
Dom is a little more complex to use compared to SAX.
Use SAX if you need to parse big data as a Stream. Use DOM if you want to hold the complete data in memory to work with it and the data-size is small enough to safely fit into memory.
For example: XSLT doesn't work with SAX because it needs to look forward in the data-stream while reading it. So it uses DOM even if that leads to memory-issues with big data.
Hope that helped :-)
