Hello iggy ziggy(strange name!)
Please read
Designing WebServices- SUN Blue prints 4th chapter XML Processing & 5 th chapter Client Design, where lot of scenarios are discussed talking about when to use xml and when to use custom objects..
It doesnt matter even if you have non-java client.. Their tools generate client classes in corresponding languages given the wsdl document..
You dont have to distribute java classes to clients.. From the wsdl
doc, the tool can create the necessary input, output classes..
But there are other things that you have to consider in deciding to use xml or java classes for input & output. for e.g
1) Data Size - How much data is being communicated back and forth per request/transaction (1K, 1M, 10M)?
2) Data frequency - How often will the data be "queried", daily, weekly, each time a user clicks some button on a UI?
3) Data Type - Structured text based data, images, engineering files etc?