I'm currently doing co-op at IBM RTP campus and I've applied for full-time conversion for my current position. There are other opening positions that I'm also interested in.

1. Entry level cognitive developer
2. Entry level backend developer
3. Entry level devops engineer

Here are my questions:

1. What's the difference in salaries (starting salary, raise, salary range based on same level experience) among those three positions? I'm asking this because I've heard that frontend developers are likely to get less than backend developers.
2. IBM is my first and only internship/co-op experience, so I can't say what I'm interested in. Is any of three better than other two, career growth wise?
3. I'm interested in machine learning but don't want to do client-facing data science jobs. I'm looking for a developer position that requires ML knowledge. Is cognitive developer the right direction?