Thanks Johnrgb, I looked them both up and saw that Manet was older, but still went with Monet. What a sneaky question! I think, on reflection, that you are right, too late now, posted answers this morning!
By 1874 Manet's reputation as experimental artist and leader of the Impressionists was firmly established. The Cafe Guerbois, near his studio became the gathering spot for Monet, Renoir, Sisley and Degas and although Manet presided over the regular meeting and debates held at the cafe, he was not enthusiastic about his role as leader of the avant-garde.
Thanks to Lector and Slaney, I think the whole fiendishness of this question is that it is a matter of personal opinion. Sure, Manet was the older of the two, but was he really the originator of impressionism? Monet picked it up and ran with it, and I think was the better artist, but does that make him the originator? probably not, in which case I have put the wrong answer. I think art historians can argue for ever on this. As you say, we will find out on Saturday!