One thing I guess you already knew: Spring is a suite of frameworks and Spring MVC is only one of those frameworks. They all rely on Spring core. But there are other frameworks inside Spring: Spring MVC (similar to Struts), Spring security (acegi), JMS templates, DB templates (for JPA, Hibernate, Ibatis,
JDBC...), Spring Workflow...
I agree with Sonny. Go for Spring and Spring MVC as a first solution. And then, consider if you go for Struts 2, or you prefer to go for GWT or a similar one, because knowing Spring MVC you don't really need Struts 2. Struts 2 is another way of doing what Spring MVC already does. Both Spring MVC and Struts 2 are page-based MVC frameworks, so once you know Spring MVC the first reason to learn Struts could be just that you need it for a job.
I've got the feeling there's little future for page-based MVC frameworks. Today everybody wants Web 2.0 and that's not the concept of pages, but AJAX based applications. I think soon we'll all be using Echo 2, GWT, jQuery...