These chickens have been selectively bred by someone who realy knows how to select the best breeding flock. I don't know if they selected just for color but I suspect they also selected for egg laying ability. The stock they started with was not leghorns. It was chickens bred to lay better than leghorns. And I don't know the traits in the original Araucanas they started with. By now, you may be wondering if I know anything, and that may be a legitimate question. I'm not even finished telling you what I don't know.
I don't know the quality or traits of the mille fleur leghorn flock you are talking about. Leghorns should lay fairly large white eggs and lay several of them, so at least I know something. That gene that makes the Mille Fleur speckling or mottling is a recessive gene, so it will not show up in the first generation if they are crossed with any chicken that does not have it. And I don't know the quality or purity of those Aracaunas. I sure don't know the color of those Araucanas so I cannot tell you what colors or patterns the offspring will be but they should not have the mille fleur speckling.
But assuming the leghorns are pretty typical for leghorns and the Araucana are pretty typical for what Araucana should be, what you should wind up with is a chicken that lays blue eggs. They should lay more eggs and larger eggs that the Auracana lay, but maybe not as well or as big as the leghorns. The adult chickens will probably not be very large, so they would not be really good for meat, although you can eat any chicken.
I don't know any real benefit in making that cross as to which is the hen and which is the rooster from an egg laying perspective, but I'd use the leghorn rooster over the Araucana hens. I'm not confident that the Araucana are pure Araucana and pure for the blue egg gene. If you only hatch eggs from the Araucana and those eggs are blue, then you know that the hen has at least one blue egg gene. If you use an Araucana rooster over the leghorn hens, you really don't know if he has any blue egg genes unless you are certain he is pure Araucana. When you say some are tuffed and some are not, that raises my suspicions.
I don't know the quality or traits of the mille fleur leghorn flock you are talking about. Leghorns should lay fairly large white eggs and lay several of them, so at least I know something. That gene that makes the Mille Fleur speckling or mottling is a recessive gene, so it will not show up in the first generation if they are crossed with any chicken that does not have it. And I don't know the quality or purity of those Aracaunas. I sure don't know the color of those Araucanas so I cannot tell you what colors or patterns the offspring will be but they should not have the mille fleur speckling.
But assuming the leghorns are pretty typical for leghorns and the Araucana are pretty typical for what Araucana should be, what you should wind up with is a chicken that lays blue eggs. They should lay more eggs and larger eggs that the Auracana lay, but maybe not as well or as big as the leghorns. The adult chickens will probably not be very large, so they would not be really good for meat, although you can eat any chicken.
I don't know any real benefit in making that cross as to which is the hen and which is the rooster from an egg laying perspective, but I'd use the leghorn rooster over the Araucana hens. I'm not confident that the Araucana are pure Araucana and pure for the blue egg gene. If you only hatch eggs from the Araucana and those eggs are blue, then you know that the hen has at least one blue egg gene. If you use an Araucana rooster over the leghorn hens, you really don't know if he has any blue egg genes unless you are certain he is pure Araucana. When you say some are tuffed and some are not, that raises my suspicions.