This question is about data visualization, but ultimately it deals with usability and user expectations, so I felt it was appropriate to post it here.
Imagine you are doing a comparison over time between two entities, one entity (or series) represents 'you' and another time series that represents some benchmark entity. The user's analysis question is to try and get a clear picture of how 'you' compares to the benchmark entity over time. In other words, the delta between the two series over time. To do this I opted to flatten one of the series (turn it into a baseline) and make the y-axis show 'delta from baseline'. My question is, which of the two series should be the baseline?
Here is a concrete example:
Here is the basic visual (two series, with the difference highlighted in blue):
--- Option A - baseline is 'you' series:
--- Option B - baseline is 'benchmark' series: