The best curriculum is the one you USE!!!
I met a new homeschool mom the other day at the park and she was stressing (as we all did/do) on what to use for her son (3 1/2) when he got older. I told her my best advice I ever got was the above. If a curriculum promises to make your child a scholar and has testimonies to prove even the "average" child will excel with it that's great... but, if you don't ever use it because it's so time consuming or boring or what have you, you're better off with something else. Actually using something even if it's not "advanced" is going to get you much farther than not using the "best" and building guilt as it gathers dust on the shelf. Next time you're looking at curriculum think about the "fit" with your family. Be honest with yourself. Will you really use it? If not, move on.