1. I'm using this tool from last 4 yrs, trained many.. as of now you can't get any better tool for free.
2. I have also used ReadyAPI (paid version of SoapUI) which is much easy to use.
3. I would like to recommend to all beginners to start with soapUI to get better hands on with Groovy.
4. Most of my client like the training we provided on soapUI for their project.
5.Most importantly Smartbear team regularly stays in contact with you for training and improvements in the application for their latest enhancements.
6. Latest version soapUI can do most of the job which are available in enterprise version.
7. It can test Both SOAP & REST API services, it provides output in XML format.