Ahem! Cough cough! I think we're drifting here, if having fun, so I hope it's okay if I get back to the original question...
I don't think it was a case of favouritism, unless it's slanted towards humanity. The impression I got was that the Elves were to be sort of our big brothers and sisters (whether it worked out that way or not is another matter), to look after us, hence the reason for their being created first. They got the "immortality" if you like, at least till the end of the world, but no guarantee of anything better after a long, wearisome eternity. Humans, on the other hand, got the "gift of Illuvatar". We mightn't like it much, but it was supposed to go with having a soul and escape from "the circles of the world." Just imagine being dragged kicking and screaming into re-birth and more of the same, more lembas, more artistic stuff...