I prefer Daniel Boulud, but not by a huge margin. They're both French, they're both informal, and they're similarly priced. To me, the dishes at Daniel Boulud are a little more interesting, and a little better. DB's atmosphere is good for dinner, especially if you snag a table outside.
However, if at all possible, go to Bouchon for breakfast. It's the best in town.
For details of my meals at these places (and others), go to my page of restaurant reviews at http://home.comcast.net/~lasvegasvaca... .
Whichever you choose, know that DB Brasserie will be closed from June 4th to July 4th for renovations. My vote is for Bouchon. The patio area is open now, great food and atmosphere.
I prefer Bouchon by a fairly large margin; I thought the food was better and I really like the room and the patio, if it is available. I do agree that they are very similar in menu and price point.