Things to look before you choose an SEO firm (according to priority)
1. The article submission, social bookmarking, directory submission are outdated. The first thing is to check whether they provide any unique services that others don't.
2. Time is the important factor. Check out how fast they can do that (without any compromise to quality)
3. Pricing-- obviously it should be affordable.
4. Testimonials from other clients.
5. Finally any previous records
I find all these qualities at www.submitinme.com