Google has posted a comparison to Spring here
http://code.google.com/p/google-guice/wiki/SpringComparison
To be fair that will be biased since considering who wrote it so
you should also read this article by the Spring in Action author
http://jroller.com/habuma/entry/guice_vs_spring_javaconfig_a
I think by reading both articles you get a fairly balanced comparison.
Keep in mind this is a comparison of Guice to the relevant parts of Spring (DI only). Spring incorporates way more than just DI. If you have need for these things (like I do) I prefer to just use Spring for all of it as there is no comparable features in Guice.