Webtest is the more established project with its first release in 2007. Webtest is provided by Canoo as a free open source plugin to Grails. The tests are run via an Ant script that packages together the test cases and runs through each one.
Functional-test is a relatively new project with its first release in early 2009. Functional test is basically the same as webtests however instead of using the Ant-based scripts everything is based on Junit and implemented in plain old java or groovy.
We’ve chosen to proceed with using the Junit-based plugin for our HTTP integration tests. Our primary reason in deciding to use Junit is that it integrates well with our other unit-based tests which also use Junit instead of using disparate frameworks for the various types of tests. While this plugin may be newer it’s traffic on the mailing lists is growing and substantial.