Seam vs Spring is a topic for many TSS articles and JRoller blogs to come. Here's my quick take.
Neither technology is directly responsible for getting data either into or out of the database. You'll need a persistence provider for that. Once you have one, you'll likely look to Spring or Seam to help you tie all the pieces of your overall web application together.
In order to evaluate whether Spring or Seam is better for your project, take a look at the examples and demos that ship with both and decide which fits your use cases and existing code base better.