Doing things manually is labour intensive and can result in a lot of mistakes. CMS's can automate a lot of this - title tags, meta tags, alt tags, no dead links and up to date menus just to name a few. The time you've saved can then be used to go in manually and optimize the bits the CMS missed.
They are all very similar and it depends on the theme and plugins you use to optimize for SEO as well as manual fixes, however I would suggest looking at wordpress for ease of use.