Okay, so let me add this. I like the area provided by my 3 foot deep brooders better. It is a nice squarish area, instead of a long rectangle. They both work fine, but for larger groups I like to put them in the 3 foot deep brooder.
However, if I have to catch them regularly, I put them in the 2 foot deep brooder. My 3 foot deep brooder works fine for my older friendly birds who just need to be locked up temporarily. But for young chicks that will run and squawk and try to get away, it is really hard to catch them.