Benjamin Franklin didn’t actually suggest that the turkey should be the bird depicted on the Great Seal of the United States of America. But he took a little comfort that the eagle on the seal looked like a turkey. Writing to his daughter, Franklin lectures about the shady ethical character of the eagle:
For my own part, I wish the bald eagle had not been chosen the representative of our country. He is a bird of bad moral character. He does not get his living honestly. You may have seen him perched on some dead tree near the river, where, too lazy to fish for himself, he watches the labor of the fishing hawk. And when that diligent bird has at length taken a fish and is bearing it to his nest for the support of his mate and young ones, the bald eagle pursues him and takes it from him.
With all this injustice, he is never in good case, but like those among men who live by sharping and robbing, he is generally poor and often very lousy. Besides he is a rank coward: the little king bird, not bigger than a sparrow, attacks him boldly and drives him out of the district. He is therefore by no means a proper emblem for the brave and honest Cincinnati of America  who have driven all the king birds from our country …
I am on this account not displeased that the figure is not known as a bald eagle, but looks more like a turkey. For the truth, the turkey is in comparison a much more respectable bird, and withal a true original native of America … He is besides, though a little vain and silly, a bird of courage and would not hesitate to attack a grenadier of the British Guards who should presume to invade his farm yard with a red coat on.
(edited to conform to contemporary American grammar and diction)
As if commenting on the Book of Leviticus, Franklin’s sentiment is one of animalian moralizing worthy of the Epistle of Barnabas:
Neither shalt thou eat eagle nor falcon nor kite nor crow. Thou shalt not, he saith, cleave unto, or be likened to, such men who know not how to provide food for themselves by toil and sweat, but in their lawlessness seize what belongeth to others, and as if they were walking in guilelessness watch and search about for someone to rob in their rapacity, just as these birds alone do not provide food for themselves, but sit idle and seek how they may eat the meat that belongeth to others, being pestilent in their evil-doings.
– Epistle of Barnabas 10:4
I’m with Ben Franklin when he later actually suggested the rattlesnake was the proper animal to depict the “temper and conduct of America” (or at least what the temper and conduct of America should be). However, these days, the stereotype of the turkey does seem rather apropos some of the time. :-p
 The “brave and honest Cincinnati of America” was a newly formed society of the officers of the American War for Independence at that time.