http://www.amazon.com/s?ie=UTF8&keywords=eagerest&index=blended&page=1 check with amazon, i found the word "eagerest"
It doesn't appear in the Oxford English Dictionary. It does seem to have some American usage - that doesn't necessarily make it acceptable English!
The thing is that this is the third form of comparison or something like that... it called superb form if I'm not mistaken and there are rule like if the word is short it changed like easy -->easier--> the easiest and if it is ling then difficult--> more difficult--> the most difficult and there is like good -->better--> the best Unfortunately I don't remember how these ways of word formation are called but the thing is that according to the rule "eagerest" is the right variant, but taking into consideration the difference between American And GB English and taking into consideration that simple fact that "the most eager" is simpler to say.... this is just the way it evolved