I own both of these books & Julia Child's "The Way To Cook" is my hands down favorite. My copy is falling apart I've used it so often, & her "Steam Roasted Goose with Port Wine Gravy" has been our traditional Xmas dinner since the day the book first came out. What's particularly nice about it is that it will first give a basic "master" recipe, & then follow that with several building-block variations to turn that one recipe into several completely different meals. Lots of room for easy experimentation & lots of fun without sacrificing traditional concepts.
Martha's book is nice (I was gifted with a copy for Xmas), but just isn't in the same league as Julia's. In addition, you have to be careful with Martha's cookbooks (I have nearly all of them), as the recipes don't always cook true & you have to always be at the ready to make adjustments. (And this isn't only my opinion - it's been a well-known fact for years re: her books.)
Don't get me wrong - both books are nice. But as far as good basic traditional knowledge & foolproof recipes & methods, I'd DEFINITELY choose Julia & save Martha's tome for another time.