Puzzle: Which one will fill first?

Which squares fill first with fluid?


Created by Imgurian CorneliaXaos:

So.. this was, like… 3+ hours to make.. It's 1269 frames long… and was a "joy" to animate by hand… next time I write a program to do this for me…. the physics.. they're not super-correct for actual fluids.. I ignore air pockets in places and fill the containers "fast" after the bottom-most row was complete… still.. it would look something like this if you left the sink running. :P