The only tools I know in this regard are Mantis and JIRA. Mantis seems ok-ish, and while at least the "intro"-screen of Redmine reminded me a bit on it, Redmine looks more compact and has a good deal more features. JIRA, on the other hand, aside of the licensing problems, is really nice, especially once you use it together with other stuff from the same company.
Anyway, Redmine, at least the sandbox demo, has a nice compact look'n'feel to it, and it seems to cover the important stuff you need. What you really should look into are the SVN hooks, so you know which commit relates to which issue. Another thing you might be interested in is the Eclipse Mylyn support for Redmine, if you are using Eclipse as a development platform, that is.
As I haven't worked with either Trac nor Redmine I can't really tell you which one is better. Best you make a list of features you need for your stuff, maybe add another list of features you may want to use in the future and then decide if you switch or not