int() probably doesn't guarantee that the rounding will necessarily be rounded up or down. I would usually expect an int() function to simply truncate the value -- effectively rounding down -- but it also wouldn't be out of the question for it to round to the nearest integer value instead, and given the behaviour isn't specifically listed in the manual it's also possible that this implementation detail might be changed at some point and should not be relied on to always stay the same.
However, let's assume that there's no technical
difference and that both functions will have the same effect: each function still expresses a different intent
, and you should use whichever more accurately expresses what you intend on doing. You int() when you want to convert a value to an integer, round() if you want to round to the nearest integer value, and floor() or ceil() if you'd like to round up or down.
By choosing a function that clearly expresses your intent you increase readability of your code and reduce the need for explanatory comments.