Site Categories Vs. Blog Types?

What is the actual difference between the 'Blog Types' plugin and the 'Site Categories' plugin?

From what I gather they both seem to do very similar things.

My needs:
1. I am going to want to be able to display just one 'type' of blogs in a widget or a page listing.
2. Have access to blog meta tags which will allow me to write my own custom functions targeting specific 'groups' of blogs.

Basically I suppose I need to know which is the farthest along code wise, and which is the most flexible. They are just so similar on the outside that it's confusing having both of them available.