Originally posted by Darrell Bulloch:
How would one know which method to use?
By trying to understand each option, one will choose the best for his/her system.
SAAJ =>
Soap with Attachment API for java = >
http://java.sun.com/xml/saaj/index.jsp => As you can guess, you will use it to send attachments along with the soap message.
JAX-RPC => RPC is Remote procedure call, JAX-Rpc is java api for xml based RPC. you will use to build webservices. => more info here
http://java.sun.com/xml/jaxrpc/primerarticle.html HttpURLConnection - Printwriter
There is so many free automated tools available already to writer simple to complex clients doing the job you want, Ex: Apache Axis, if they don't meet your needs, then you can write on your own.