According to the documentation on the Maven Surefire Plugin, -Dmaven.test.skipshould skip both compilation and execution of the tests. By contrast, -DskipTests just skips the test execution: the tests are still compiled.
skipTestswill compile anything in the <testSourceDirectory>, but will not execute them.
maven.test.skip will NOT compile any tests, but WILL execute any compiled tests that made their way into the <testOutputDirectory>.
So the behavior of the above 2 is opposite. Just wanted to point out that maven.test.skip doesn't skip compilation AND execution if test files are unpacked/copied/etc. into <testOutputDirectory>.
Also, depending on which version of Maven your using, there's also maven.test.skip.exec=true which additionally skips test execution similar to skipTests.