Jazz is better in the long run for two strategic reasons.  These have nothing to do with with the usual, "I like my tools better" arguments, but has to do with long term strategy towards software development.
1) Because you have choices.  If you don't like the Jazz SCM, or have a team that doesn't like Jazz SCM, you can use Subversion.  OSLC and Eclipse provide the ability to plug in a variety of software development tools into your environment, without a lot of heavyweight integrations.  This gives you flexibility now, and in the future.
2) Because you have transparency.  Jazz provides a platform for making your software development teams more transparent, and therefore more accountable.  Dashboards and web access means that stakeholders can see the status of their requests, and can track them.  It allows them to better understand the conflicting pressures a software development team is under, and pushes business decisions back into the lines of business (in the case of an IT shop).
I could go on for hours on this topic, but I will spare you.  Just see my blog entries on "Jazz, Transparency and what comes next?" (http://dtoczala.wordpress.com/2011/01/20/jazz-transparency-and-what-comes-next/), and "Collaboration and Innovation - It's not all tools" (http://dtoczala.wordpress.com/2012/06/18/collaboration-and-innovation-its-not-all-tools/).