I've only had a cursory look at Google Guice, but this is my first impression as compared with Spring, which I've used a lot more. Using Spring has actually changed the way I approach writing code.

What I like about Guice is that it is statically type-checked. Spring's xml configuration is like a dynamically typed language, and more errors slip through to later stages.

What I like about Spring is that code doesn't need to be written with any Spring-specific calls or constructs, whereas Guice requires Guice-specific annotations. If I only had to deal with code I've written, it wouldn't matter so much. However, Spring makes it hooking in code from external libraries more convenient.

Also, when using Spring, I like being able to specify every last configurable flag in the xml configuration, and anything that truly needs to be tuned can further be extracted into a properties file. Guice seems to make that level of configuration more inconvenient. Perhaps I am overlooking some mechanism, but it seems inconvenient to have to insert yet another annotation to name yet another string field that I want to configure, rather than just being able to inject beans. Guice seems to encourage having a few, high-level, injected objects, rather than every last configurable value injected.

One nice thing about Guice is that it can inject private fields, while Spring requires a public setter method. This is just a minor thing though, since, while the implementing class may have some public setters, the public interface that it is being injected as won't have those public setters. There is also constructor injection, but that is not convenient when there are many parameters to inject.