ACLs can be misleading in both xrays and MRIs. They can also heal themselves sometimes, given enough time. So, in effect, both men may be right in their diagnoses. You'll not lose a lot by waiting and seeing if things right themselves. However, having surgery when it's not entirely necessary could lead to early onset of arthritis. I would caution patience. It'll not get worse and might even get better.
BTW, I wouldn't put so much weight on a person's letters as I would on the facts of their medical practice. For instance, how many ACL reconstructions do either of these men do in a year? (500+ would be my absolute minimum) What are their good outcomes percentage-wise, and their poor outcomes. What's their infection rate? You need to ask them these questions, not just look at the diplomas on their walls! Just a suggestion!