KDP/Createspace v. Smashwords v. Scribd.

I’m looking for some advice on self-publishing platforms. For anyone who’s published or knows about using any of these platforms:
1)what’s the difference between them?
2)Which one did you like better?
3) Also, are there restrictions? I’ve heard if you publish on KDP/Createspace that they buy your exclusive rights and you can’t publish it anywhere else.

I’d love to have your input and experience (below)!