Keep in mind if money is what you are comparing, the financial health and opportunity at the ad agency needs to be examined closely as well. 20% of a small agency vs 20% of a large agency is very different.

You also need to consider how much control you like to have with your work, at 20%, you may not have the final say anymore. Consider whether or not your potential future partners have the same value and see if its a fit.

Ask yourself where do you want o be and what kind of future do you see yourself in? Like all good decisions, start with your objectives!

Hope this helps!

Jennifer Ping