I own both, they are two different software. it's like comparing apple to oranges.
Scrapebox is powerful when you want to find certain website to post comments and stuff like that, especially wordpress blogs, also finding high pr forums, but it doesn't do what BMD does.
BMD - is a real powerful tools when comes to create new accounts and submitting links to all these popular bookmarking sites like digg, fark, reddit, buzz, etc etc.
Everything is automated, so you don't need to submit them manually.
I love both software and use them regularly, definitely get decaptcher services.