In older versions of Acrobat the Constrain Proportions checkbox was above the margin dimensions boxes. That was far, far more usable for me, as 99.9% of the artwork I'm working with has uniform crop marks. I'm a keyboard user, so when the Crop dialog opens, I'll tab down to the dimensions. In previous versions I could press the space bar to check Constrain Proportions, tab to Top, type in my crop amount, tab to the next box and I was all set.

Now I have to either click Constrain Proportions separately then shift+Tab to go back up, or tab several extra times.

This isn't some make or break thing, but after using a newer version for several months, I still find myself annoyed by the new layout and having a worse user experience.