1. command line: you need a soapui gui (from installer or unpacked archive).
2. junit: you must put all soapui dependencies jar in your classpath. Currently, you have to manage this manually or use the maven plugin as dependency and use a build tool that manage transitive dependencies. You will have access to the whole soapui api which is very flexible
3. maven: you don't need soapui gui (expect for soapui pro reports), the plugin will download all dependencies. You won't have access to the whole api but this should let you cover must of use case. The available options are quite the same than with the command line tool
If you work in a team, you have external dependencies to run the test, you want to use a CI server, don't choose 1.
Doc:
command line:
http://www.soapui.org/Test-Automation/f ... tests.htmljunit:
http://www.soapui.org/Test-Automation/i ... junit.htmlmaven:
http://www.soapui.org/Test-Automation/maven-2x.html