I decided to ignore all the hype on the packages and let the BIRDS decide. I moved my backyard picnic table over to where our feeder normally lives, and I put out FIVE types of seed, all commonly available in most stores. I watched it solidly for a full day, and then more sporadically on subsequent days. The birds definitely showed which seeds they enjoyed and which they did not.
First, the basic layout. Here is a diagram of how I set up the table.

So the five types of seeds I used were:
BOSS: Black Oiled Sunflower Seeds, the common, black shell kind
SS: Shelled seeds, i.e. the insides of the sunflower seeds
MX: Mixed seeds, with sunflower amongst many other types
TH: Thistle, the little black niger seeds
CC: Cracked Corn
Page 2: The Seed Types Explained
Photos from the Experiment

