There isn't really a means to choose your maximum that is objective.
SQL only provisions what is needed by your data anyway so if you have used
The fact that the field has a 2GB capacity doesn't matter since it will only be used for 200MB of the 200MB video file you are inserting for your column data type.
Given that, unless you are certain of the precise size of each file, I would advise using varbinary(max). In this manner, you can be certain that there will be room for it and that your data won't be truncated to fit.