I think a bio-dad may generally be more cooperative. I should know better than to start a discussion that goes in this direction because it's such an emotional topic for me.

My wife put in a lot more work with her two step-sons than she has with our own 4 children and got kicked in the teeth the entire time until those boys became adults. It was tough to watch especially while feeling guilty for being responsible for putting her in the turmoil the whole time.
Meanwhile, the step-dad was always regarded by everyone as a hero who stepped up big when the bio dad (me) turned out to be a loser.